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in  2009  with  funding  from 

Boston  Library  Consortium  IVIember  Libraries 


http://www.archive.org/details/geologyofgreenmoOOpump 


LIBRARY  CATALOfUTK  SLIPS. 

United  States.     Deparlimnt  of  the  hilcriur.     (  r.  ,S.  yeoloi/U'dl  surveii.) 

Department  of  the  interior  |  —  |  Monograi)lis  |  of  tlie  |  Unit(^(l 
States  geological  survey  |  Volume  XXIII  |  [  Seal  of  tlie  depart- 
meut]  I  WasUiugtoii  |  government  printing  ofiHce  |  1S91 

Second  tUle:  United  States  geologieal  survey  |  .1.  W.  Powell 
director  |  —  |  Geol  gy  |  of  the  |  Green  monntain.s  |  in  |  Massa- 
chusetts I  by  Raphael  Pumpelly,  J.  E.  Woltf,  and  T.  Nelson  Dale  | 
[Vignette]  j 

Washington  |  government  printing  office  |  1894 

4°.    XIV,  206  pp.    2;!  pi. 


Pumpelly  (Raphael)  and  others. 

United  States  geoh)gical  survey  |  .1.  \V.  Powell  director  |  —  | 
s  Geology   |   of  the   |   Green  mountains   |   in   |    Massachusetts   |   liy 

Z  Raphael  Pumpelly,  J.  E.  Wolff,  and  T.  Nelson  Dale  |  [Vignette]  | 

a  Washington  |  governnu'ut  printing  office  |  1894 

5  4°.     XIV,  2U6  pp.    -23  pi. 

[United  States.    Deiiart ineni  of   the  intcrinr.     (P.   !i.   rjeoloijical  .iiiroey.) 
Monograph  SXllI.j 


United  States  geological  survey  |  .1.  W.  Powell  director  |  —  | 
Geology   I   of  the   |   Groen  mountains   |   in    |    Massachusetts   |   by 
Raphael  Pumpelly,  J.  E.  Wolff,  and  T.  Nelson  Dale  |  [Vignette]  | 

Washington  |  government  printing  office  |  1893 

4°.     XIV,  20li  pp.     23  pi. 

[UxiTEi)  States.    Drpartinent  u/   the  interior.     {U.  *.  ijeoloijical  aiuoey.) 
MouograpU  XXIII.  ] 


^DVERTISE]S4:ElSrT, 

[Monograph  XXIII. 1 


The  publipations  of  the  United  States  Geoloj^if  nl  Survey  are  iasned  in  apcordance  with  the  statute 
approved  March  o,  lS7iJ,  which  dechires  that — 

"  The  public-atiiiiis  of  the  Geological  Survey  shall  consist  of  the  annual  report  of  operaMous,  geo- 
logical and  economic  maps  illustrating  the  resources  and  classification  of  the  lauds,  and  reports  upon 
general  and  economic  geology  and  paleontology.  The  annual  report  of  operations  of  the  Geological 
Survey  shall  accompany  the  annual  report  of  the  Secretary  of  the  Interior.  All  special  memoirs  and 
reports  of  sai<l  Survey  shall  be  issued  in  uniform  cjuarto  series  if  deemed  necessary  by  the  Director,  but 
otherwise  in  ordinary  octavos.  Three  thousand  copies  of  each  shall  be  published  for  scientific  exchanges 
and  for  sale  at  the  ])rice  of  pulilication  ;  and  all  literary  and  cartographic  materials  received  in  exchange 
shall  be  the  property  of  the  United  States  and  form  a  part  of  the  library  of  the  organization :  And  the 
money  resulting  from  the  sale  of  such  publications  shall  be  covered  into  the  Treasury  of  the  United 
States." 

The  following  joint  resolution,  referring  to  all  goverument  publications,  was  passed  by  Congress 
Jnly7,  1882:  >  i  j         s 

"  That  whenever  any  document  or  report  shall  he  ordered  printed  by  Congress,  there  shall  be 
printed,  in  addition  to  the  number  in  each  case  stated,  the  '  usual  number '  (1,900)  of  copies  for  binding 
and  distributiou  among  those  entitled  to  receive  them." 

Except  in  those  cases  in  which  an  extra  number  of  any  publication  has  been  supplied  to  the  Sur- 
vey by  special  resolution  of  Congress  or  has  been  ordered  by  the  Secretary  of  the  Interior,  this  ottice 
has  no  copies  for  gratuitous  distribution. 

ANNUAL  REPORTS. 

I.  First  Annual  Report  of  the  IJnited  States  Geological  Survey,  by  Clarence  King.  1880.  8  '.  79 
pp.     1  map. — A  preliminary  report  describing  plan  of  orgauizaticm  and  publications. 

II.  Second  Anniuil  Report  of  the  United  States  Geological  Survey,  1880-'81,  by  ,1.  W.  Powell 

1882.  8°.  .  1  V,  588  pp.     62  pi.     1  map. 

III.  Third  Annual  Report  of  the  Unite<l  States  Geological  Survey,  1881-82,  by  .J.  W.  Powell. 

1883.  8°.     xviii,  564  pp.     67  pi.  and  maps. 

IV.  Fourth  Annual  Report  of  the  Uiuted  States  Geological  Survey,  1882-'83,  by  ,T.  W.  Powell. 

1884.  8'^.     xxxii,  473  pp.     85  pi.  and  maps. 

V.  Fifth  Annual   Report  of  the  United  States   Geological   Survey,  188.3-84,  by  .1.  \V.  Powell. 

1885.  8°.     xxxvi,  469  pp.     .58  pi.  and  maps. 

VI.  Sixth  Annual  Report  of  the  United  States  Geological  Survey,  1884-85,  by  J.  W.  Powell. 
1885.     8°.     xxix,  570  pp.     65  pi.  and  maps. 

VII.  Seventh  Annual  Keiiort  of  the  United  States  Geological  Survey,  1885-86,  by  .J.  W.  Powell. 

1888.  8°.     XX,  656  pp.     71  pi.  and  maps. 

VIII.  Eighth  Annual  Report  of  the  United  States  Geological  Survey,  1886-87,  by  J.  W.  Powell. 

1889.  8°.     2  v.     xix,  474,  xii  jip.     53  pi.  and  mpps;  1  p.  1.     475-1063  pp.     54-76  pi.  and  maps. 

IX.  Ninth  Annual  Report  of  the  United  States  Geological  Survey,  1887-'88,  by  J.  W.  Powell. 

1889.  8^.     xiii,717pp.     88  pi.  and  maps. 

X.  Tenth  Annual   Report  of  the  United  States  Geological   Survey,  1888-'89,  by  .1.  W.  Powell. 

1890.  8°.     2v.     XV,  774  p]).     98  pi.  and  maps;  viii,  123  pp. 

XI.  Eleventh  Annual  Rejiort  of  the  United  States  Geological  Survey,  1889-90,  by  •!•  W.  Powell. 

1891.  8*^.     2  V.     XV,  757  pp.     66  pi.  and  maps;  ix,  351pp.     30  pi.  and  maps. 

XII.  Twelfth  Annual  Rei)ort  of  the  United  States  Geological  Survev,  1890-'91,  liy  J.  \V.  Powell. 
1891.     8°.    2  V.     xiii,675pi).     53  pi.  and  maps;  xviii,  576  pp.     146  pi.  and  maps, 

XIII.  Thirteenth  Annual  Report  of  the  United  States  Geological  .Survev,  1891-';i2,  by  J.  \V. 
Powell,  1893.     8^^.    3  V.  =.  .  >     . 


II  ADVERTISEMENT. 

MONOGRAPHS. 

I    Lake  Bonneville,  bv  Grove  Karl  Gilbert.     1890.     i~.     xx,  438  pp.     51  pi.     1  map.     Price  $1.50. 

II.  Tertiary  History  of  the  Grand  Canon  District,  with  atlas,  by  Clarence  E.  Dutton,  Capt.,  U.  S.  A. 
1882     4"^      xiv  '%4  pp.     42  pi.  and  atlas  of  24  sheet.s  folio.     Price  $10.00. 

III.  Geology  of  the  Comstock  Lode  and  the  Washoe  District,  with  atlas,  by  George  F.  Becker. 
1882     4'^      XV  422  pp.     7  pi.  and  atlas  of  21  sheets  folio.     Price  $11.00. 

IV.  Cometock  Mining  and  Miners,  by  Eliot  Lord.     1883.     4':.     xiv,  451  pp.     3  pi.     Price  $l.oO. 

V.  The  Copper-Bearing  Kocks  of  Lake  Superior,  by  Roland  Duer  Irving.  1883.  4^.  xvi,  464 
pp.     15  1.     29  pi.  and  maps.     Price  $1.85.  ,.,,...,     ,,,.,,.        ., 

VI  Contribntious  to  the  Knowledge  of  the  Older  Mesozoic  Flora  of  A  irgiuui,  by  William  Morris 
Fontaine.     1883.     4-\     xi,  144  pp.     54  1.     .54  pi.     Price  $1.05.  .. 

VII.  Silver-Lead  Deposits  of  Eureka,  Nevada,  by  Joseph  Story  Curtis.     1884.     4^ .     xiu,  200  pp. 

^'     VIII.  Paleontology  of  the  Enr.dca  District,  by  Charles  Doolittle  Walcott.     1884.    4°.     xiii,  298 
pp.     24  1.     24  pi.     Price' $1.10.  ,   „     ,        r -kt 

IX  Brachiopoda  and  Lamellibranchiata  of  the  Earitan  Clays  and  Greeusaud  Marls  of  New 
Jersey,  by  Robert  P.  Whitfield.     1885.     4'-.     xx,  338  pp.     35  pi.     1  map.     Price  $l.lo. 

X  Dinocerata.  A  Monograph  of  an  Extinct  Order  of  Gigantic  Mammals,  by  Othniel  Charles 
Marsh.  ■  1886.     4°.     xviii,  243  pp.     56  1.     56  pi.     Price  $2.70.  ^  ^^     „         ^         .r        i      . 

XI  Geoloo-ical  Hi.story  of  Lake  Lahontan,  a  Quaternary  Lake  of  Northwestern  Nevada,  by 
Israel  Cook  Rnslell.     1885.  "4'^.     xiv,  288  pp.     46  pi.  and  maps.     Price  $1.75. 

XII.  Geology  and  Mining  Industry  of  Leadville,  Colorado,  with  atlas,  by  Samuel  Iranklin  Lm- 
nions  '  1886     4-!"  xxix,  770  pip.     45  pi.' and  atlas  of  35  .sheets  folio.     Price  $8.40. 

XIII.  Geology  of  the  Quicksilver  Deposits  of  the  Pacific  Slope,  with  atlas,  by  George  F.  Becker. 
1888     4^.     xix,  486"  pp.     7  jd.  and  atlas  of  14  sheets  folio.     Price  $2.00. 

XIV  Fo.ssil  Fishes  and  Fossil  Plants  of  the  Triassic  Rocks  of  New  Jersey  and  the  Connecticut 
Valley,  by  John  S.  Newberrv.     1888.     4^^.     xiv,  152  pp.     26  pi.     Price  $1.00. 

'XV.  The  Potomac  or  Younger  Mesozoic  Flora,  by  William  Morris  Fontaine.  1889.  4^.  xiv, 
377  pi).     180  pi.     Text  and  ))lates"bonnd  separately.     Price  $2.50. 

XVI.  The  Paleozoic  Fishes  of  North  America,  by  John  Strong  Newberry.     1889.     4>^.     340  pp. 

53  pi.     Price  $1.00.  ,  ,    ,      r        t  i..-.^   ,,     t;- 

XVII.  The  Flora  of  the  Dakota  Gronj),  a  posthumous  work,  by  Leo  Lesquereux.  Edited  by  i-. 
H.  Kmiwlton.     1891.     4^.     400  pp.     66  pi.     Price  $1.10. 

XVIII  Gasteropoda  and  Cephalo]ioda  of  the  Raritan  Clays  and  Greensand  Marls  of  New  Jersey, 
by  Robert  P.  Whitfield.     1891.     4--.     402  pj).     .50  pi.     Price  $1.00.  ,  „.   ,.  ,       „,       ,„ 

XIX.  The  Penokee  iron-Bearing  Series  of  Northern  Wisconsin  and  Michigan,  by  Roland  D. 
Irving  and  C.  R.  Van  Hise.     1892.     -l- .     xix,  534  pp.     Price  $1.70. 

XX.  Geologyof  the  Eureka  District,  Nevada,  with  an  atlas,  by  Arnold  Hague.     1892.     4^.     xvii, 

419  pp.     8  pi.     Price  $5.25.  ,      ^  ,„   ,,       ,  c.      i 

XXI.  The  Tertiary  Rhynchophorous  Coleopteia  of  the  United  States,  by  Samuel  Hubbard  Scud- 
der.     1893.     4^.     xi,  206*  iip. 'l2  pi.     Price  90  cents. 

XXII.  A  Manual  of  Topograpliii'  Methods,  by  Henry  Gannett,  chief  topographer.  1893.  4^. 
XIV.  300  pp.  18  pi.    Price  $1.00  ,      ,„  ,,      .n  x.  , 

XXIII.  Geology  of  the  Green  Mountains  in  Massachusetts,  by  Raphael  Piiinpelly,  P.  Nelson  Dale, 
and  J.  E.  Wolff.     1894.     4'^.     xiv,  206  pp.     23  pi.     Price  $1.30 

In  press: 

XXIV.  Mollusca  and  Crustacea  of  the  Miocene  Formations  of  New  Jersey,  by  R.  P.  Whitfield. 

In  preparation : 

— Sauropoda,  by  0.  C.  Marsh. 

— Stegosanria,  by  O.  C.  Marsh. 

— Brontotheridiie,  by  O.  C.  Marsh. 

—Report  on  the  Denver  Coal  Basin,  by  S.  F.  Emmons. 

—Report  on  Silver  Clitt"  and  Ten-Mile  Mining  Districts,  Colorado,  by  S.  F.  Emmons. 

—The  Glacial  Lake  Agassiz,  by  Warren  Uphani. 

BULLETINS. 


L  Hyperstheue-Andesite  and  on  Tricliuic  Pyroxene  in  Augitic  Rocks,  by  Whitman  Cross, 
ilogical  Sketch  of  Buffalo  Peaks,  Colorado,  by  S.  F.  Emraous.     1883.     8".     42  pp.     2  pi. 


1.  On 
with  a  Geolo 
Price  10  cents. 

2.  Gold  and  Silver  Conversion  Tables,  giving  the  coining  values  of  troy  ounces  of  fine  metal,  etc., 
computed  by  Albert  Williams,  jr.     1883.     8^.     8  pp.     Price  5  cents. 

3.  On  the  Fossil  Faunas  of  the  Upper  Devonian,  along  the  meridian  of  76<^  30',  from  Tompkins 
County,  IL  Y.,  to  Bradford  County,  Pa.,  by  Henry  S.  Williams.     1884.     8°.     36  pp.     Price  5  cents. 

'4.  On  Mesozoic  Fossils,  by  Chaales  A.  White.     1884.     8-.     36  pp.     9  pi.     Price  5  cents. 
5.  A  Dictionary  of  Altitudes  in  the  L'nited  States,  compiled  by  Henry  Gannett.     1884.     8^.     325 
pp.     Price  20  cents. 


ADVERTISEMENT.  Ill 

6.  Elevations  in  tbe  Dominio'n  of  Canada,  by  J.  W.  Speuoer.     1884.     8'^.     43  pp.     Price  5  cents. 

7.  Mapoteca  Geologica  Americana.  A  Catalogue  of  Geological  Maps  of  An  erica  (North  anil 
South),  1752-1881,  in  geographic  and  chronologic  order,  by  Jules  Marcou  and  John  Belknap  Marcou. 

1884.  8>J.     184  ])p.     Price  10  cents. 

8.  On  Secondary  Enlargements  of  Mineral  Fragments  in  Certain  Rocks,  by  R.  D.  Ir^'iug  and  C. 
R.  Van  Hise.     1884.     8-^.     56  pp.     6  pi.     Price  10  cents. 

9.  A  Report  of  work  done  in  the  Washington  Laboratory  during  the  tiseal  year  1883-'84.  F.  W. 
Clarke,  chief  chemist;  T.  M.  Chatard,  assistant  chemist.      1884.     8"^.     40  pp.     Price  5  cents. 

10.  On  the  Cambrian  Faunas  of  North  America.  Preliminary  studies,  by  Charles  Doolittle  Wal- 
cott.      1884.      8".      74  pp.      10  pi.      Price  5  cents. 

11.  On  the  Quaternary  and  Recent  Mollusca  of  the  Great  Basin;  with  Descriptions  of  New 
Forms,  by  R.  Ellsworth  Call.  Introduced  by  a  sketch  of  the  Quaternary  Lakes  of  the  Great  Basin, 
by  G.  K.  Gilbert.     1884.     8°.     66  pp.     6  pi.     Price  5  cents. 

12.  A  Crystallograx>hic  Study  of  the  Thinolite  of  Lake  Lahontan,  by  Edward  S.  Dana.  1884.  8". 
34  pp.     3  pi.     Price  5  cents. 

13.  Bonn<larie8  of  the  United  States  and  of  the  several  States  and  Teiritories,  with  a  Historical 
Sketch  of  the  Territorial  Changes,  by  Henry  Gannett.     1885.     8'^'.     135  pp.     Price  10  cents. 

14.  The  Electrical  and  Magnetic  Properties  of  the  Iron-Carburets,  by  Carl  Barns  and  Vincent 
Strouhal.     1885.     8^'.    258  pp.     Price  15  cents. 

15.  On  the  Mesozoic  and  Cenozoic  Paleimtology  of  California,  by  Charles  A.  White.  1885.  8'^. 
33  pp.     Price  5  cents. 

16.  On  the  Higher  Devonian  Faunas  of  <  )ntario  County,  New  York,  by  John  M.  Clarke.  1885.  8°. 
86  pp.     3  pi.     Price  5  cents. 

17.  On  the  Development  of  Crystallization  in  the  Igneous  Rocks  of  Washoe,  Nevada,  with  Notes 
on  the  Geology  of  the  District,  by  Arnold  Hague  and  Joseph  P.  Iddings.  1885.  8^.  44  pp.  Price  5 
cents. 

18.  On  Marine  Eocene,  Fresh- water  Miocene,  and  other  Fossil  MoUnsca  of  Western  North  America, 
by  Charles  A.  White.     1885.    8".     26  pp.     3  pi.     Price  5  cents. 

19.  Notes  on  the  Stratigraphy  of  California,  by  George  F.  Becker.   1885.   8".   28pp.   Price5cent8. 

20.  Contributions  to  the  Mineralogv  of  the  Rockv  Mountains,  by  Whitman  Cross  and  W.  F.  Hille- 
brand.     1885.     8'-.     114  jip.     1  pi.     Price' 10  cents. 

21.  The  Lignites  of  the  Great  Sioux  Reservation.  A  Report  on  the  Region  between  the  Grand 
and  Moreau  Rivers,  Dakota,  l>y  Bailey  Willis.     1885.     8"-.     16  pp.     5  pi.     Price  5  cents. 

22.  On  New  Cretaceous  Fossils  from  California,  by  Charles  A.  White.  1885.  8<^.  25  pp.  5  pi. 
Price  5  cents. 

23.  Observations  on  the  Junction  between  the  Easteru  Sandstone  and  the  Keweenaw  Series  on 
Keweenaw  Point,  Lake  Superior,  by  R.  D.  Irving  and  T.  C.  Chamberlin.  1885.  8<^.  124  pp.  17  pi. 
Price  15  cents. 

24.  List  of  Marine  Mollusca,  comprising  the  Quaternary  fossils  and  recent  forms  from  American 
Localities  between  Cape  Hatteras  and  Cape  Roque,  including  the  Bermudas,  by  William  Healey  Dall. 

1885.  8'^'.     336  pp.     Price  25  cents. 

25.  The  Present  Technical  Condition  of  the  Steel  Industry  of  the  United  States,  by  Phiueas 
Barnes.     1885.     8-^.     85  pp.     Price  10  cents. 

26.  Copper  Smelting,  by  Henry  M.  Howe.     1885.     8^.     107  pp.     Price  10  cents. 

27.  Report  of  work  done  in  the  Division  of  Chemistry  and  Physics,  mainlv  during  the  liscal  vear 
1884-'85.     1886.     8^.     80  ]>p.     Price  10  cents. 

28.  The  Gabbros  and  Associated  Hornblende  Rocks  occurring  in  the  Neighl)orhood  of  Haltinjore, 
Md.,  by  George  Huntington  Williams.     1886.     8'-.     78  pp.     4  pi.    Price  10  cents. 

29.  On  the  Fresh-water  Invertebrates  of  the  North  American  Jurassic,  by  Charles  A.  White.  1886. 
8^.     41  pp.      4  ]il.     Price  5  cents. 

30.  Second  Contribution  to  the  Studies  on  the  Cambrian  Faunas  of  North  America,  by  Charles 
Doolittle  Walcott.     1886.     8^.     369  pp.     33  pi.     Price  25  cents. 

31.  Systematic  Review  of  our  Present  Knowledge  of  Fossil  Insects,  including  Myriapods  and 
Arachnids,  l)y  Sanniel  Hubbard  Scudder.     1886.     8^.     128  jip.     Price  15  cents. 

32.  Lists  and  Analyses  of  the  Mineral  Springs  of  the  United  States;  a  Preliminarv  Stndv,  by 
Albert  C.  Peale.     1886.     8'-.     235  pp.     Price  20  cents. 

33.  Notes  on  the  Geology  of  Northern  California,  by  J.  S.Diller.     1886.    8^.    23  pp.    Price  5  cents. 

34.  On  the  relation  of  th<'  Laramie  MoUiiscan  Fauna  to  that  of  the  succeeding  Fresh-water  Eocene 
and  other  groups,  by  Charles  A.  White.     1886.     8'^.     .54  pp.     5  pi.     Price  10  cents. 

35.  Physical  Properties  of  the  Iron-Carburets,  by  Carl  Barns  and  Vincent  Strouhal.  1886.  8-\ 
62  pp.     Price  10  cents. 

36.  SubsidenceofFineSolidParticlesiuLifiuids,byCarlBarus.    1886.    8°.    58pp.    PricelOcents. 

37.  Types  of  the  Laramie  Flora,  by  Lester  F.Ward.     1887.     8'^.     3.54  pp.     .57  pi.     Price  25  cents. 

38.  PeridotiteofEUiottCouuty,  Kentucky,  by  J.  S.  Diller.     1887.     8^.    31pp.    Ipl.    Price5cents. 

39.  The  Upper  Beaches  and  Deltas  of  the  Glacial  Lake  Agassiz,  by  Warren  Upham.  1887.  8"^. 
84  pp.     1  pi.     Price  10  cents. 

40.  Changes  in  River  Courses  in  Washington  Territory  due  to  Glaciatlon,  by  Bailey  Willis.  1887. 
8*-.     10  pp.     4  pi.     Price  5  cents. 

41.  On  the  Fossil  Faunas  of  the  Upper  Devonian — the  Genesee  Section,  New  York,  bv  Henry  S. 
Williams.     1887.     8-.     121  pp.     4  pi.     Price  15  cents. 

42.  Report  of  work  done  in  the  Division  of  Chemistry  and  Phvsics,  niaiulv  during  the  fiscal  year 
1885-'86.     F.W.Clarke,  chief  chemist.     1887.     8^.     152  pp.     Ipl.     Price  15  cents. 


IV  ADVERTISEMENT. 

43.  Tertiary  and  Cretaceous  Strata  of  the  Tuscaloosa,  Tombigbee,  and  Alaliania  Rivers,  by  Eugene 
A.  Smith  and  Lawrence  C.  .Johnson.     1887.     8^.     189  pp.     21  pi.     Price  15  cents. 

44.  Bibliography  of  North  Americau  Geology  for  1886,  by  Nelson  H.  Dartou.  1887.  8'^.  35  pp. 
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In  preparation : 

118.  .Studies  in  the  (Structure  of  the  Green  Mountains,  by  T.  Nelson  Dale. 

The  Moraines  of  the  Mi.ssouvi  Coteau  and  their  attendant  deposits,  hy  .James  Edward  Todd. 

A  Bibliograjihy  of  Paleobotany,  by  David  White. 

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To   THE   DiRECTOI!   "IF  THE 

United  States  Geological  Survey, 

Washington,  D.  C. 
Washington,  D.  C,  March,  1SU4. 


U1 

^ 

Tin 

en 

LiJ 

CE 

O 

Vol -^3 


DEPARTMENT   OF   THE    INTERIOR 


MONOGRAPHS 


OF  THE 


United  States  Geological  Survey 


VOLUME    XXIII 


WASHIIfGTON 

GOVERNMKNT    FEINTING    OFFICE 

189  4 


\jo  ('23 


UNITED  STATES  GEOLOGICAL   SURVEY 

J.   W.   POWELL,   DIRECTOR 


GEOLOGY 


OF   THE 


GEEEN    MOUNTAINS 


IN 


MASSACHUSETTS 


BY 


RAPHAEL  PUMPELLY,  J.  E.  WOLFF,  AND  T.  NELSON  DALE. 


'sJ^ 


WASHINGTON 

GOVERNMENT   PRINTING  OPFICB! 
1894 


CONTENTS, 


Page- 
Letter  of  transmittal xi 

Preface xili 

Part  I. — Geology  of  the  Green  mountains  in  Massachusetts,  by  Raphael  Pumpelly. 

General  description 5 

Age  and  structure 7 

Correlation 9 

Part  II. — The  geology  of  Hoosac  mountain  and  adjacent  territory,  by  J.  E.  Wolff. 

Introduction 41 

Topographic  work 41 

Topography 41 

Description  of  rocks  of  Hoosac  mountain 44 

The  Stamford  gneiss 45 

The  Vermont  formation 48 

The  Hoosac  schist 59 

The  Stockbridge  limestone 64 

Amphibolites 65 

Geology 69 

The  Hoosac  tunnel 69 

The  region  embracing  the  central  part  of  Hoosic  mountain 72 

The  northern  and  eastern  schist  area 86 

The  region  south  of  Cheshire  and  of  the  Hoosic  valley 88 

Hoosic  valley  schist 97 

The  region  around  Clarksburg  mountain  and  Stamford,  Vermont 98 

General  conclusions , 102 

Part  III.— Mount  Greylock:  its  areal  and  structural  geology,  by  T.  Nelson  Dale. 

Outline  of  this  paper 125 

Historic  131 

Physiographic 133 

Structural 136 

Types  of  structure 138 

Correlation  of  cleavage  and  stratification 155 

Pitch  157 

Structural  principles 157 

Structural  transverse  sections 158 

Lougitutional  sections 175 

Resumd,  structural 177 

Lithologio  stratigraphy ,,..,, 179 

V 


VI  CONTENTS. 

Page. 

Pctrograpliy 181 

Areal  and  structural 191 

Relation  of  geology  to  topography 192 

Appendix  A:  Stone  hill  near  Williamstown 197 

Appendix  B:  New  Ashford 202 


ILLUSTRATIONS. 


Page. 
Pl-ATK   I.  Map  of  Greylock  and  Hoosao  mountains Frontispiece. 

II.  General  map  showing  the  relation  of  the  Greylock  series  to  the  Hoosac  mountain 

rooks 10 

III.  Structural  relations  of  the  Hoosac  series 14 

IV.  Detailed  map  of  western  crest  and  slope,  Hoosac  mountain 40 

V.  Geologic  profiles,  Hoosac  mountain 70 

VI.  Geologic  profiles,  generalized,  Hoosac  mountain 80 

VII.  Thin  sections,  white  gneiss 110 

VIII.  Thin  sections,  white  gneiss  and  albite  schist 112 

IX.  Thin  sections,  diorite  and  amphibolite 114 

X.  Thin  sections,  quartzite  conglomerate  and  crumpled  metamorphic  conglomerate 116 

a  .  View  north  over  crest  of  Hoosac  mountain 118 

■  b  \  Profile  of  Hoosac  mountain  from  Spruce  hill  south,  looking  west . .  ^ 118 

XII.  Mount  Greylock,  eastern  side 130 

XIII.  Mount  Greylock,  western  side 132 

XIV.  Southern  summit  of  Mount  Greylock 134 

XV.  Southern  side  of  Mount  Greylock 136 

XVI.  Southern  end  of  Ragged  mountain 160 

XVII.  The  north-south  part  of  Hopper 192 

XVIII.  Greylock  sections,  A,  B,  C,  D 

XIX.  Greylock  sections,  E,  F 

XX.  Greylock  sections,  G,  H,  I 

XXI.  Greylock  sections,  J,  K,  L,  M 

XXII.  Greylock  sections,  IJ,  O 

XXIII.  Greylock  longitudinal  sections,  P,  Q,  R 

Fig.    1.  The  Stamford  dike,  showing  the  Cambrian  conglomerate  deposited  in  dike  fissure 11 

2.  The  Stamford  dike,  plan 11 

3.  Correlated  columns  of  the  Hoosac  and  Greylock  rocks 13 

4.  Anticlinal  arch  across  Hoosic  river  between  North  Adams  and  Briggsville 15 

5.  Ideal  section  east  of  Cheshire,  showing  lateral  transition  of  limestone  to  schist 17 

6.  Diagram  of  structure,  summit  of  the  Buttress 22 

7.  Crumpled  structure  in  albite-schist 23 

8.  Map  showing  the  varying  character  of  Cambrian  rocks  around  the  Hoosac  core 31 

9.  View  from  Hoosac  mountain 42 

10.  Profile  of  Hoosao  mountain  ( western  crest) 43 

11.  Profile  of  Hoosac  mountain  ( western  slope) 44 

12.  Granitoid  gneiss 45 

VII 


a 


a, 
o 


VIII  ILLUSTRATIONS. 

Page. 

Fig.  13.  Metamorphic  conglomerate   showing  crushing 48 

14.  Metamorphic  conglomerate,  showing  shape  of  pebbles 49 

15.  Metamorphic  conglomerate;  flattened  pebbles 50 

16.  Metamorphic  conglomerate ;  round  and  flat  pebbles 51 

17.  Metamorphic  conglomerate,  banded  variety 53 

18.  Metamorphic  conglomerate,  typical 55 

19.  Metamorphic  conglomerate,  showing  large  pebbles 57 

20.  Conglomerate ;  cliff 58 

21.  Albite-schist,  Hoosac  schist 59 

22.  Albite-schist,  Hoosac  schist 61 

23.  Albite-schist,  Hoosac  schist '. 62 

24.  Mount  Holly  amphiliolite _ g5 

25.  Mount  Holly  amphibolite .-...- _ 66 

26.  Mount  Holly  crumpled  amphibolite 67 

27.  Contact  of  grauif old  gneiss  and  metamorphic  couglomerate 73 

28.  Contact  of  grauitoid  gneiss  and  quartzite,  Stamford  dike,  looking  north 100 

29.  Contact  of  grauitoid  gneiss  and  quartzite,  Stamford  dike,  looking  east 101 

30.  Northwestern  side,  Mount  Greylock 136 

31.  Albitic  sericite-schist  in  contact  with  limestone 138 

32.  Sericite  schist  with  two  foliations,  in  contact  with  limestone I39 

33.  Sericite  schist ;  specimen  with  two  foliations 139 

34.  Thin  section  illustrating  origin  of  cleavage I.j0 

35.  Sketch  of  ledge  south  of  Sugarloaf,  showing  cleavage  in  both  limestone  and  schist 140 

36.  Limestone  block  with  cleavage ;  Sugarloaf 141 

37.  Limestone  ledge  with  cleavage ;  east  of  Sugarloaf 141 

38.  Weathered  limestone  from  East  mountain 142 

39.  Polished  surface  of  limestone  shown  in  Fig.  38 142 

40.  Weathered  limestone  with  mica  in  cleavage  planes 143 

41.  Specimen  of  sericite-schist  showing  stratitication  and  cleavage.  Bald  mountain 144 

42.  Specimen  of  sericite-schist  showing  only  cleavage,  Symonds  peak 144 

43.  Section  of  specimen  shown  in  Fig.  42 I45 

44.  Section  of  specimen  of  sericite-schist,  top  of  Mount  Greylock I45 

45.  Microscopic  drawing  of  sericite-schist,  top  of  East  mountain 146 

46.  Specimen  of  sericite-schist,  one-fourth  mile  south  of  Mount  Greylock 147 

47.  Diagrams  showiug  relation  of  quartz  lamiuiv  to  cleavage 148 

48.  Ledge  of  sericite-schi.st,  junction  of  Gulf  and  Ashford  brooks 148 

49.  Part  of  ledge  shown  in  Fig.  48 I49 

50.  Section  of  sericite-schist  with  quartz  lamin;e ;  from  Goodell  hollow 150 

51.  Ledge  of  mica-schist  in  Readsboro,  Vermont,  svith  ([uartz  in  both  foliations 151 

52.  Sericite-schist  with  two  cleavages,  Goodell  hollow 1,52 

53.  Section  of  sericite-schist,  one- fourth  mile  south  of  Greylock  summit 153 

54.  Sericite-schist,  one- fourth  mile  southwest  of  Greylock  summit 154 

55.  Diagram  showing  fault  between  schist  and  limestone t 154 

56.  Section  of  sericite-schist.  Bald  mountain  spur 155 

57.  Diagram  showing  relation  of  cleavage  to  stratification 156 

58.  Diagram  showing  relation  of  cleavage  to  stratification 156 

59.  Quartz  laminae  in  schist,  west  side  of  Deer  hill 157 


.  ILLUSTRATIONS.  IX 

Page. 

Fig.  60.  Minor  pitching  limestone  folds 157 

61.  Cross-section  G 160 

62.  Section  of  syucline  at  soutli  end  of  Ragged  mountain 161 

63.  Cross-section  H 166 

64.  Cross-section  I 166 

65.  Cross-sections  A,  B 169 

66.  Cross-section  F 171 

67.  Cross-sections  J,  K,  L 172 

68.  Structure  in  schist,  south  side  of  Saddle  Ball 173 

69.  Cross-sections  M,  N,  O 173 

70.  Structure  in  schist,  west  of  Cheshire  reservoir 174 

71.  Longitudinal  sections  P,  Q,  R 175 

72.  Continuity  of  the  folds  ou  the  Grey  lock  sections 178 

73.  Albitic  sericite-schist :  typical  Greylock  schist 188 

74.  Outline  sketch  of  Round  rocks 194 

75.  Sketch  of  Greylock  mass  from  southwest 195 

76.  Cross-sections  S,  T,  U.  Stone  hill 198 

77.  Sketch  of  protruding  limestone  anticline.  New  Ashford 202 

78.  Diagram  map  of  Quarry  hill.  New  Ashford 202 

79.  Cross-section  of  Quarry  hill.  New  Ashford 203 


LETTER  OF  TRANSMITTAL. 


Department  of  the  Interior, 

U.  S.  Geological  Survey,  Archkan  Division, 

Newport,  E.  L,  January  18, 1892. 

Sir  :  I  have  the  honor  to  transmit  herewith  a  memoir  on  the  Greology 

of  the  Green  mountains  in  Massachusetts. 

Your  obedient  servant, 

Raphael  Pumpelly, 

Geologist  in  charge. 
Hon.  J.  W.  Powell, 

Director  U.  S.  Geological  Survey. 

XI 


PREFACE. 


The  following  memoir  is  the  result  of  the  fieldwork  of  the  Archean 
Division  of  the  U.  S.  Geological  Survey  in  northwestern  Massachusetts, 
during  the  years  1885,  1886,  and  1887. 

The  conclusions  put  forth  were  all  arrived  at  before  1888,  but  the 
publication  of  them  was  delayed  until  they  should  be  either  confirmed  or 
corrected  by  the  results  of  further  study  in  southwestern  Massachusetts 
and  in  central  Vermont. 

The  progress  of  our  survey  of  western  New  England  has  fully  con- 
firmed our  interpretation  of  the  facts  observed  in  the  Hoosac  mountain  and 
Grreylock  area.  It  has  been  our  intention  to  keep  wholly  clear  of  the 
Taconic  controversy,  and  to  confine  our  efforts  to  accurate  study  and  inter- 
pretation of  structure.  In  the  first  part  I  have  given  a  statement  of  the 
sequence  and  bearing  of  the  results  and  have  advanced  some  theoretical 
views  in  explanation  of  the  sudden  disappearance  of  the  Lower  Silurian 
limestone  against  the  western  base  of  the  Grreen  mountain  anticline.  I 
have  also  advanced  a  hypothesis,  supported  by  observation  in  the  northern 
and  southern  Appalachians,  to  explain  (through  the  presence  of  a  previously 
deeply  disintegrated  land  surface)  the  apparent  conformable  transition 
between  Archean  or  pre-Gambrian  gneisses  and  Cambrian  quartzite.  This 
almost  insuperable  difficulty  is  met  with  in  many  of  the  great  crystalline 
areas  of  the  world,  in  passing  from  Archean  or  eruptive  masses  to  the  clastic 
crystalline  schists. 

The  second  part  treats  of  Hoosac  mountain — the  central  or  crystalline 
range  of  the  Grreen  mountains.  The  field  work  was  performed  by  Dr.  J. 
E.  Wolff,  Mr.  B.  T.  Putnam,  and  myself.  The  analysis  of  the  results,  the 
petrographic  study,  and  the  presentation  are  by  Dr.  Wolff.     Mr.  Putnam 


XIV  PREFACE. 

had  contributed  largely  to  the  sum  of  the  work.     His  early  death  in  1886 
deprived  the  Survey  of  one  of  its  most  accurate  and  thouglitful  geologists. 

The  third  part  deals  with  the  Grreylock  synclinorium — made  up  of  the 
Cambrian-Silurian  quartzite,  limestones,  and  schists,  which  are  the  offshore 
time  equivalents  of  the  white  gneisses  and  schists  of  Hoosac  xnountain. 
The  held  work  was  done  by  Mr.  T.  Nelson  Dale,  assisted  in  part  of  the 
area  by  Mr.  William  H.  Hobbs.  The  analysis  of  the  results  and  the  pre- 
sentation are  by  Mr.  Dale. 

As  during  the  first  two  years  we  had  not  yet  the  benefit  of  the  new 
topographic  map  of  Massachusetts,  our  work  was  delayed  by  the  necessity 
of  making  our  own  maps.  This  was  done  in  part  by  Messrs.  Putnam  and 
Wolff,  assisted  by  Mr.  Yocum.  Later,  Mr.  Josiah  Pierce  made  a  detailed 
topographic  survey  of  the  western  flank  of  Hoosac  mountain  which  forms 
the  geographic  basis  of  PI.  iv. 

Mr.  C.  L.  Whittle  was  also  connected  with  the  work  under  Dr.  Wolff 
during  the  season  of  1887. 

Mr.  William  H.  Hobbs  acted  as  assistant  to  Mr.  Dale  during  one  season 
and  a  part  of  another  in  the  work  on  Greylock  and  was  engaged  inde- 
pendently during  the  rest  of  the  second  season  on  the  coloring  of  the 
northwestern  part  of  the  Greylock  sheet. 

I  have  mentioned  in  its  proper  place  the  fact  that  we  owe  to  Mr.  C.  D. 
Walcott  the  determination  of  the  age  of  our  basal  quartzite. 

R.  P. 


PA^RT    I 


GENEIUL  STRUCTURE  AND  CORRELATION. 


By  RAPHAEL  PTJMPELLY. 


MON  XXIII 1 


CONTENTS. 


Page. 

General  description : 5 

Age  ami  stnieture - 7 

Correlation 9 


ILLUSTRATIONS, 


Page 

Pl.    I.  Map  of  Greylock  and  Hoosac  Mountains Frontispiece. 

11.  General  map  showing  relation  of  the  Greylock  series  to  the  Hoosac.  mountain  rocks 10 

III.  Structural  relations  of  the  Hoosac  series - 14 

Fig.  1.  The  Stamford  dike,  showing  Caoibrian  conglomerate  deposited  in  dike  fissure 11 

2.  The  Stajnford  dike,  plan 11 

S.  Correlated  columns  of  the  Hoosac  and  Greylock  rocks ,  .  13 

4.  Anticlinal  arch  across  Hoosic  river  between  North  Adams  and  Briggsville 15 

5.  Ideal  sectiou  east  of  Cheshire,  showing  lateral  transition  of  limestone  to  schist 17 

6.  Diagram  of  structure,  summit  of  the  buttress 22 

7.  Crumpled  structure  in  albite-schist 23 

8.  Map  showing  the  varying  character  of  Cambrian  rocks  around  the  Hoosac  core 31 

3 


GEOLOGY  OF  THE  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

GENERAL  STRUCTURE  AND  CORRELATION. 


By  Raphael  Pumpelly 


GENERAL  DESCRIPTION. 


The  Green  mountains,  nearly  coinciding  with  the  prolongation  of  the 
axis  of  the  Archean  core  of  the  Appalachians  through  western  New  Eng- 
land, stand  between  the  less  disturbed  fossiliferous  Paleozoic  strata  of  New 
York  and  the  highly  crystalline  rocks  of  New  England.  They  consist  of 
three  principal  structural  elements :  The  Green  mountains  (Hoosac  moun- 
tain) ;  the  Taconic  range,  lying  several  miles  to  the  west ;  and,  between 
these,  the  great  valley.  But  the  whole  region  between  the  Hudson  and  the 
Connecticut  has  very  properly  been  placed  by  Dana  in  one  mountain  sys- 
tem. I  shall  therefore  follow  Dana  and  distinguish  between  a  central  or 
axial  ridge,  flanked  by  an  eastern  belt  extending  to  the  Connecticut,  and  a 
western  belt  extending  to  the  Hudson,  though  what  I  shall  have  to  say  refers 
mainly  to  the  central  belt  and  the  neighboring  portion  of  the  western  belt. 

The  Green  mountain  range  is  composed  of  crystalline  schists,  which 
our  results  show  to  be  of  Cambrian  and  Lower  Silurian  age,  resting  on  pre- 
Cambrian  rocks,  and  it  was  long  ago  shown  by  Edward  Hitchcock  to  have 
an  anticlinal  structure.  The  Avestern  edge  of  this  axial  range  is,  for  long 
stretches,  marked  by  a  loft}^  brow  of  quartzite,  and  for  this  reason  the 
mountains  present  a  very  steep  flank  on  the  west.  At  the  base  of  this 
western  flank  lies  what  is  known  as  the  valley  of  Vermont  or,  in  Massachu- 


6  (iREKN  MOUNTAINS  IN  MASSACHITSETTS. 

setts,  the  Berkshire  valley.  This  valley  has  a  floor  of  crystalline  limestone, 
often  a  saccharoidal  marble  of  Cambrian  and  Lower  Silurian  age,  on  which 
stand  long  island-like  ridges  of  schist,  of  Lower  Sihman  age,  and  it  extends 
with  a  breadth  of  several  miles  from  northern  Vermont  to  Alabama.  The 
schist  is  everywhere  underlain  by  the  limestone,  which  is  marked  by 
the  fertility  of  its  soil ;  and,  along  its  whole  length,  its  wealth  of  limonite 
ores  has  for  more  than  a  century  formed  the  basis  of  important  iron  indus- 
tries. Li  the  folded  strata  of  this  valley  belt  in  Vermont  and  Massachusetts, 
subsequent  erosion  has  left  island-like  mountains,  sometimes  of  anticlinal, 
but  generally  of  svncliual  structure,  with  more  or  less  pitch  in  their  axes. 
Instances  of  the  latter  are  Eolus  (Dorset),  Anthony,  Greylock,  Everett, 
etc.,  rising  to  1,500  or  3,000  feet  above  the  valley,  and  surrounded  to  a 
greater  or  less  height  above  the  base  by  the  limestone,  and  hea^^ly  capped 
with  the  weather-resisting  schist.  Instances  of  anticlinal  structure  are  the 
less  elevated  pine  hill  near  Rutland  and  the  ridge  which  connects  it  with 
Danby  hill  in  Vermont. 

On  the  west,  this  limestone  valley  has  for  a  wall  the  Taconic  moun- 
tains, with  peaks  rising  1,500  to  2,500  feet  above  the  valley.  This  is  a 
synclinal  range  of  the  same  Lower  Silurian  schist,  but,  having  its  trough 
at  a  lower  level,  the  limestone  foundation  appears  only  at  the  base. 

Turning  now  to  the  region  east  of  the  axis  of  the  Green  mountain 
anticline,  we  find  no  great  and  continuous  depression  comparable  to  that  of 
the  valley  of  Vermont  until  we  reach  the  Connecticut  valley  ;  and  this  is 
occupied  by  much  later  strata — Triassic  resting  on  Devonian.  This  eastern 
region  is  a  very  roughl}'  mountainous  mass  of  schist,  and,  though  of  plateau 
origin,  is  crossed  by  deeply  cut  transverse  valleys,  which  receive  longi- 
tudinal tributaries,  whose  courses  are  determined  in  the  main  by  the 
geologic  structure  of  the  territorj^.  All  along  the  eastern  edge  of  the  axial 
belt  of  the  mountains  there  occur  such  narrow,  longitudinal  valleys,  and 
as  they  contain,  more  or  less  continuously,  beds  of  limestone  of  either 
Cambrian  or  Lower  Silurian  age,  they  define  the  eastern  limit  of  the  Green 
mountain  range  proper,  with  less  topographic  but  with  equal  geologic 
sharpness. 


GENERAL  STliUCTURE  AND  (JORKBLATION.  ^ 

AGE  AND   STRUCTURE. 

In  Ijeginniug  work  on  the  geology  of  New  England,  two  facts  were 
apparent — that  from  the  Grreen  mountains  eastward  the  rocks  were  all  highly 
metamorphosed  and  crystalline;  and  that  onlj"  in  two  or  three  localities  had 
fossils  been  found,  and  in  these  places  the  rocks  were  so  much  disturbed 
that  it  seemed  hopeless  to  use  them  as  starting  points  for  the  general  work. 
I  became  convinced  that  our  hopes  of  determining  the  age  of  the  New 
England  rocks  lay  in  using  the  Green  mountains  as  a  bridge.  In  following 
this  plan  we  were  immediately  met  by  the  fact  that  on  the  main  ridge — our 
proposed  bridge — the  rocks  are  not  only  highly  metamorphosed  and  their 
structure  the  reverse  of  simple,  but  that  the  western  edge  of  the  ridge  marks 
an  abrupt  lithologic  change  between  the  character  of  the  rocks  of  the 
mountain  and  those  of  the  valley,  with  the  exception  of  the  younger  schists, 
which  in  places  cap  both  the  axial  range  and  the  valley  hills.  On  the  west 
the  great  limestone  and  an  underlying  great  quartzite  come  eastward  to  the 
base  of  the  mountain,  while  a  careful  reconnaissance  showed  no  trace  of  these 
rocks  as  such  upon  the  mountain,  nor  of  such  a  combination  on  the  eastern 
side. 

This  difficulty,  which  met  the  earlier  surveys,  had  led  to  various 
hypotheses  in  which  faults  and  overturns  played  an  important  part.  And 
while* the  rocks  of  this  main  ridge  were  assigned  by  different  eminent 
geologists  to  ages  ranging  from  the  Sillery^  to  Huronian  and  Laurentian,^ 
the  residuum  of  opinion  has  been  of  late  in  favor  of  Archean  or  at  least 
pre-Cambrian  age.  The  problem  was  undoubtedly  too  difficult  to  be 
solved  without  more  ample  means  than  were  at  the  disposal  of  our  pre- 
decessors. 

It  was  evident  that  our  first  and  hardest  work  would  be  to  find  the  key 
to  the  structure  of  the  range.  For  this  purpose  I  sought  a  region  where  the 
western  edge  should  present,  instead  of  a  straight  line,  as  many  bay-like 
curves  as  possible,  and  where  the  structure  of  the  ridge  itself  should  show 
folds  with  pitching  axes.     I  hoped  in  such  a  region  to  eliminate  the  difficul- 


'  Logan  colors  them  as  Sillery  on  the  Geological  map  of  Canada,  1866. 

"  C.  H.  Hitchcock :  geological  sections  across  New  Hampshire  and  Vermont.     Bull.  Am.  Mus. 
Nat.  Hist.,  vol.  I,  New  York,  1884 


8  GREE:sr  MOUNTAINS  IN  MASSACHUSETTS. 

ties  introduced  by  possible  faults,  as  well  as  the  temptation  to  infer  their 
existence;  and  also  in  case  of  pitching  folds  to  get,  through  radiating  cross 
sections,  a  knowledge  of  the  true  order  of  bedding. 

These  conditions  were  found  well  presented  in  the  northwestern  corner 
of  Massachusetts.  Here  the  western  edg-e  of  the  main  ridg-e  coraino-  down 
from  Vermcfnt  makes  a  sharp  turn  eastward  around  Clarksburg  mountain; 
then  after  resuming  for  several  miles  a  straight  southerlj^  course  it  curves 
back  westward  to  bend  around  the  Dalton  hills.  Opposite  this  bay  stands 
Greylock  mountain,  which  Emmons  and  Dana  had  shown  to  be  a  great 
synclinal  mass.  The  greater  and  higher  part  of  this  Greylock  mass  of 
Lower  Silurian  rocks  rises  to  the  east  of  the  chord  of  the  arc  that  is  formed 
by  this  bay-like  curve.  Again,  Hoosac  mountain,  east  of  this  bay,  exhibits 
a  variety  of  distinct  rocks  in  folds,  the  axes  of  which  show  a  persistent 
northerly  pitch.  And  in  addition  to  this  I  hoped  for  much  aid  from  the 
great  tunnel,  which,  in  1865,  I  had  examined  for  the  state  of  Massachu- 
setts. With  a  length  of  nearly  5  miles,  it  pierces  the  mountain  through  its 
whole  breadth  at  a  depth  of  over  1,000  feet,  and  the  fact  that  the  tunnel 
was  driven  from  both  ends  and  from  two  intermediate  shafts  gave  assurance 
that  the  dumps  would  supply  unaltered  material  for  the  petrographic  study 
of  the  various  rocks  in  all  their  variation  of  habit.  As  there  Avas  then  no 
topographic  map  of  the  i-egion  we  were  obliged  to  locate  all  of  our  work 
by  transit  survey.  During  the  first  two  seasons,  in  company  with  my 
assistants,  Mr.  B..T.  Putnam  and  Mr.  J.  E.  Wolff,  I  made  thorough  recon- 
naissances of  the  area  in  question,  and,  to  obtain  as  much  light  as  possible, 
these  excursions  were  extended  southward  to  the  Highlaiids  east  of  the 
Hudson  and  northward  to  centi-al  Vermont. 

We  had  found  that  the  mass  of  Hoosac  mountain  consists  of  a  core  of 
coarsely  crystalline  granitoid  gneiss,  overlain  in  some  places  by  a  conglom- 
erate, in  others  by  line  grained, white  gneisses.  Above  the  conglomerate 
and  white  gneisses  Ave  had  found  a  great  thickness  of  biotitic  and  sericitic 
schists,  containing  either  macroscopic  or  microscopic  albite,  in  both  un- 
twinned  and  simple  twinned  crj^stals.  At  all  the  contacts  of  this  whole 
series  there  appeared  distinct  structural  conformability. 

On  Clarksburg  mountain  Ave  had  found  the  same  coarse  granitoid  gneiss, 


GENERAL  STEUCTURE  AND  CORRELATION.  9 

covered,  apparently  conformably,  by  a  true  quartzite.  At  the  base  of  the 
Dalton  hills  the  quartzite  Avas  found  to  conformably  underlie  the  great 
Cambro-Silurian  limestone,  wliich  in  its  turn  forms  the  base  of  Greylock, 
and  this. limestone  was  found  to  Be  conformably  overlain  on  Greylock  by 
a  great  thickness  of  scliists,  identical  in  character  with  those  overlying*  on 
Hoosac — here  the  conglomerate  and  there  the  white  gneiss — with  no  inter- 
vening limestone  or  quartzite.  Again,  we  had  found  that  these  white 
gneisses  contained  apparently  iuterstratified  beds  of  these  same  schists. 

CORRELATION. 

Having  made  it  a  rule  that  all  correlation  of  strata  and  interpretation 
of  structure  should  be  decided  solely  upon  observed  structural  relations, 
there  was  nothing  to  be  done  but  patiently  to  work  out  the  structiu'e,  step 
by  step,  using  lithologic  similarities  as  clews  only. 

The  reconnaissances  showed  that  the  Green  mountains  are  wholly 
made  up  of  crystalline  schists,  and  that  one  or  more  of  the  horizons  of 
these  must  vary  in  the  most  jjrotean  manner  in  the  external  habit  of  its 
rocks,  while  on  either  side  of  the  range'  the  rocks  retain  their  respective 
characteristics  with  relatively  little  change.  One  of  the  earlier  observa- 
tions on  the  western  brow  of  Hoosac  mountain  had  been  the  superposition 
of  the  coarse  granitoid  gneiss  over  the  white  g-neiss  at  a  well-marked  con- 
tact and  with  structural  conformity  of  lamination.  On  the  other  hand,  in 
the  tunnel,  this  same  granitoid  gneiss  appeared  as  a  central  core,  fiirtiier 
east  than  the  geologic  meridian  of  the  surface  outcrop.  This  core  Avas 
found  in  the  tunneP  to  be  flanked  on  each  side  by  the  conglomerate  over- 
lain by  the  albitic  schist.  If  the  structure  were  as  simple  as  the  tunnel 
section  seemed  to  indicate  it  would  point  to  two  horizons  of  the  granitoid 
gneiss,  and  connect  this  rock  and  the  white  gneiss  in  age.     An  important 

'  Diuui  pointed  out  iu  1872  tlie  abrupt  lateral  transitions  between  the  quartzite  and  schists  of 
Berkshire  county.     (Ami.  Jour.  .Sci.,  1872,  p.  368.) 

2  This  tunnel  is  lined  with  masoury  at  irregular  intervals  to  such  an  extent  that  a  large  part  of 
the  rock,  especially  of  the  more  interesting  western  half,  is  hidden.  The  walls  are  covered  to  a  depth 
of  an  inch  with  soot.  In  addition  to  this,  geologic  work  was  made  extremely  dangerous  by  the  fact 
that  the  smoke  was  so  dense  that  even  our  thirteen  torches  were  invisible  across  the  tunnel,  and  the 
noise  of  trains  running  30  miles  an  hour  was  not  audible  until  the  engine  was  within  a  few  yards  from 
us.  Notwithstanding  these  difficulties  we  managed  to  find  the  important  contacts,  except  at  the 
■western  end,  where  they  were  bricked  over. 


10  GREEN  MOUNTAINS  IN  MASSAOHUSETTS. 

point  was  therefore  gained  when  the  hypothesis  advanced  to  us  by  Mr. 
Putnam  that  the  surface  exposure  of  granitoid  gneiss  was  a  flat,  overturned 
anticlinal  fold  was  corroborated  by  Mr.  Wolff.  Mr.  Wolff  also  discovered 
that  the  schist  beds  in  the  white  g^neiss  on  the  western  flank  belong  to  the 
series  above  the  wliite  gneiss,  and  are  simply  remnants  left  in  compressed 
troughs  overturned  to  the  west  under  the  overtmnied  anticline  just  men- 
tioned. 

The  next  step  was  made  by  Mr.  Wolff  in  the  determination  that  the 
white  g-neisses  are  clastic  rocks,  while  the  coarse  granitoid  gneiss  shows  no 
trace  of  clastic  origin.  This  pointed  to  a  closer  relation  between  the  white 
gneiss  and  the  conglomerate,  from  the  fact  that  one  or  the  other  was  found 
to  overlie  the  granitoid  gneiss.  This  question  also  was  settled  by  Mr.  Wolff 
by  tracing  out  the  lateral  transition  from  the  conglomerate  into  the  white 
gneiss. 

Finallv  the  upward  transition  from  the  white  gneiss  and  from  the  con- 
glomerate into  the  schist  was  observed. 

Messrs.  Putnam  and  Wolff  had  observed,  and  I  had  traced  later  at  several 
points  on  Clarksburg  mountain,  a  strict  conformability  between  the  lamina- 
tion of  the  granitoid  gneiss  and  that  of  the  overlying  conglomerate  and 
quartzite,  the  continuation  of  the  great  quartzite  belt  of  Vermont ;  and  later 
Mr.  Walcott  had  found,  near  the  same  contact,  numerous  casts  of  OlcneUus, 
showing  the  lower  part  of  the  quartzite  to  be  of  Low^er  Cambrian  age.  Later, 
Mr.  Wolff,  in  tracing  this  quartzite  northward  along  the  eastern  flank  of  the 
granitoid  gneiss  of  Clarksliurg  mountain,  found  it  to  pass  by  lateral  transi- 
tion along  the  strike  into  well-defined  white  gneisses  like  those  of  Hoosac 
mountain.  Later  still  a  similar  transition  was  observed  between  the  true 
quartzite  and  the  Hoosac  white  gneiss  on  the  northern  side  of  the  Dalton 
hills. 

There  still  remained  to  be  explained  the  nature  of  the  relation  between 
the  granitoid  gneiss  and  the  overlying  clastic  rocks,  and  the  conformability 
that  exists  between  the  stnicture  of  the  granitoid  and  that  of  the  overljang 
rocks.  Prof.  Emerson,  working  on  the  map  in  Hinsdale,  found  an  area  of 
granitoid  gneiss  overlain  by  the  conglomerate,  and  concluded,  from  the  re- 
lation of  the  two  rocks  over  broad  areas,  that  they  are  there  structurally 


U.S.GEOLOGrCAL  SURVEY: 


MONOGRAPH  XXII PL  II- 


SHOWING  THE  RELATION  OF  THE  GRFiXOCK  SERIES  TO  THE  HOOSAC  MOUNTMN  ROCKS. 

BY  RAPHAEL  PUMPELLY. 


Scale, 125000 


=iMiles 


1891. 


GENERAL  STRUCTURE  AND  CORRELATION. 


11 


unconformable.  At  about  the  same  time  Mr.  Wolff  had  found  the  two  dikes 
of  eruptive  basic  rock  in  Stamford  in  the  g-ranitoid  gneiss  and  at  its  contact 
with  the  quartzite.     (Figs.  1  and  2.) 


J?  'i 


N 

A 


Fio.  1. — The  Stamford  dike,  showing  the  Cambrian  conglomerate  deposited  in  dike  fissure;  (7, 
conj;l"iiifriite;  c.  l(^^ve^  layers  of  conglomerate  rendered  schistose  by  admixture  of  material  from 
the  altrre<l  dike;  d,  diah:ise  of  the  dike  rendered  schistose  hy  metamor]ihisni :  p.  nltercil  dike  ma- 
terial ;  */.  pre-Ciiiubrian  ;;Taiiitoid  jrueiss. 

We  could  hardly  have  wished  for  better  evidence  than  that  offered  by 
one  of  these.  At  the  contact  the  quartzite  strikes  N.  40°  E.,  dips  50°  SE. 
The  dike  strikes  N.  60°  W.,  between  vertical  Avails;  but  the  rock  of  the  dike 
has  undergone  changes  that  have  given  it  a  lamination,  and  the  planes  of 
this  strike  N.  35°  W.  and  dip  45°  eastei'ly.  The  structure  of  the  granitoid 
gneiss  is  here  quite  irregular  and  obscure.  No  trace  could  be  found  of  the 
dike  cutting  into  the  quartzite,  and  as 
this  is  continuou.sly  exposed  on  both 
sides,  the  possibility  of  its  absence  by 
faulting  was  eliminated.  But  there  is 
more  direct  positive  evidence  in  the  fact 
that  the  quartzite  beds  thicken  and  sag 
down  over  the  dike — indeed,  into  the 
dike  fissure,  as  Mr.  Whittle  and  I  found 
by  digging.  The  evidence  is  conclu- 
sive, as  I  satisfied  myself  during  several 
visits,  that  the  Cambrian  transgression 
found  here  a  fissure,  either  open  or  filled 
with  a  rotten  dike,  which  was  washed 
out  to  a  depth  of  several  feet  and  refilled  with  beach  sand  and  pebbles, 
the  dark  material  contributed  by  the  dike  increasing  toward  the  bottom. 
The  sudden  thickening  and  sagging  of  the  quartzite  over  the  fissure,  taken 


Fig.  2. — The  Stamford  dike,  plan,  c, conglomerate; 
d,  dike  rock,  metamorphic.  with  foliation;  e,  altered 
dike  material;  g,  Stamford  gneiss. 


12  GREEN  MOUNT AmS  IN  MASSACHUSETTS. 

in  connection  with  the  mixture  of  dike  material  and  sand,  and  the  stoppmg 
of  the  dike  at  the  quartzite,  prove  suificieutly  the  pre-Cambrian  age  of  the 
granitoid  gneiss.  And  this  is  emphasized  by  the  fact  that  both  the  quart- 
zite and  white  gneiss  are  frequently  conglomerates. 

The  structural  conformability  of  which  I  have  spoken  above  is  due 
simply  to  the  generally  parallel  lamination  that  has  been  forced  upon  the 
rocks  of  the  region  by  the  folding. 

We  had  now  established  the  fact  that  in  this  part  of  the  Green  mountains 
the  eolunm  in  the  main  range  consists  of  a  Lower  Cambrian  quartzite-con- 
glomerate-white-gneiss  formation,  resting  with  a  time  break  ujDon  a  coarse 
granitoid  gneiss,  and  conformably  overlain  by  a  great  thickness  of  schists. 

Parallel  with  the  study  of  Hoosac  mountain,  that  of  Greylock  was  carried 
on  by  Mr.  T.  Nelson  Dale,  assisted,  for  a  time,  by  Mr.  W.  H.  Hobbs.  This 
mass  was  shown  to  consist  of  a  great  lower  crystalline  limestone,  overlain 
by  a  heavy  mass  of  schists,  above  which  another  thick  mass  of  limestone 
was  overlain  hj  still  another  great  mass  of  schist,  the  whole  column  contain- 
ing about  2,000  feet  of  limestone,  and  2,500  to  4,000  feet  of  schist.  These 
estimates  are  based  on  measui'ements  of  areas  that  have  been  subjected 
to  lateral  pressure,  and  of  course  do  not  claim  to  represent  the  original 
thickness. 

Lower  Silurian  fossils  have  been  found  in  the  continuation  of  a  part  of 
the  lower  limestone  in  Vermont.  Mr.  Dale  found  the  Greylock  limestone 
and  schists  conformable  throughout  and  exhibiting  vertical  transitions. 

It  seemed  almost  impossible  to  find  points  where  the  actual  stratigraphic 
relation  of  the  limestone  to  the  quartzite  could  be  observed,  but  I  was  for- 
tunate in  finding  such  a  place  on  Lachines  creek,  near  Berkshire  station. 
Later,  by  means  of  digging,  which  was  done  here  under  Mr.  Putnam,  it  was 
shown  not  only  that  the  quartzite  and  limestone  are  structurally  conform- 
able, but  that  they  are  bound  together  by  vertical  transition  through  calca- 
reous flaggy  quartzites.  We  have  here  in  an  overturned  fold,  with  easterly 
dip,  the  Stockbridge  limestone  dipping  under  the  older  Cambrian  quartzite 
formation.  The  limestone  proper  is  succeeded  toward  the  quartzite  by 
flaggj?^  quartz  schists,  and  these  by  a  heavy  development  of  schistose  calca- 
reojas  quartzite.     East  of  this  the  quartzite  becomes  friable,  and  has  here 


GENEEAL  STKUCTUKE  AN1>  COREELATIOK 


13 


been  excavated  as  the  well-kuown  Berkshire  sand.  About  100  feet  east  of 
this  we  find  an  outcrop  of  vitreous  qiuirtzite.  The  next  outcrops — okler 
and  300  or  400  feet  eastward  and  dipping  50°  easterly — show  a  schistose 
quartzite  overlain  by  an  older  and  more  slaty  bed  of  the  same;  and  this  by 
a  very  coarsely  feldspathic  quartzite  followed  by  another  bed  of  schistose 
quartzite,  and  this  by  a  feldspathic  biotite-schist.  Representing  these  in 
their  normal  succession  we  have — 

Stockbridge  liiuestoue. 
Flaggy  quartz-schists. 
Schistose  calcareous  quartzite. 
,  Saudy  (juartzite  (friable). 

Vitreous  quartzite. 
Covered  (300  or  400  feet). 
Schistose  quartzite. 
Schistose  quartzite,  more  slaty. 
Very  feldspathic  quartzite. 
Schistose  quartzite. 
Feldspathic  biotite-schist. 

HoosacMt. 


GrvjlockMt. 


Mclloyvspipc  2jtm£S6oTW , 
Sei^k.?}Ltre    Sch  LsL 


f^rtrr-/;,-!--: 


Howe  'ScfUst. 


Ifoosfxc  Schist, 


Quiu-tzUeConfflomerate., 
Sfajri/oT'cL  Gneuf^. 


Fig.  3.— Correlated  columns  of  the  Hooa  'C  and  Greylock  rocks. 

We  now  had  both  the  Hoosac  and  Greylock  columns  complete,  and 
both  springing  from  the  same  conformably  underlying  Cambrian  quartzite 
(see  Fig.  3). 

A  glance  shows  one  point  of  difference — the  entire  absence  of  limestone 
in  the  Hoosac  column.     But  on  the  other  hand,  we  have  the  observed  con- 


14  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

tiuuity  of  deposition  from  the  quartzite  upwai'd  in  each  column,  and  we 
have  also  petrographic  identity  in  the  schists  of  the  two  columns. 

Prof  Emmons  attempted  to  explain  the  similarity  of  the  Greylock 
schists  to  those  of  Hoosac  mountain  by  deriving  the  supposedly  younger 
Greylock  beds  from  the  destruction  of  the  supposedly  older  Hoosac  rocks, 
but  Mr.  Wolff  finds,  under  the  microscope,  not  only  no  evidence  to  sup- 
port the  idea  of  such  derivation  for  the  Greylock  schists,  but  that  the 
principal  constituent  minerals  of  these  schists  were  in  each  column  all 
crystallized  in  place.  Early  in  the  course  of  the  work  it  was  proved  that 
the  limestone  was  not  present  as  such  in  the  Hoosac  column.  But  at 
two  points  near  Cheshire  harbor,  and  east  of  North  Adams,  we  found  schist 
outliers. extending  out  from  the  Hoosac  column,  and  at  the  extreme  western 
ends  conformably  related  to  the  great  limestone;  in  one  case  occupying  a 
'  synclinal  trough  in  it,  and  in  the  other  either  capping  it  or  interbedded  in  it. 

Almost  at  the  beginning  of  the  survey,  altliough  we  had  as  yet  none 
of  the  proofs  above  given  as  to  the  equivalence  of  the  valley  quartzite  with 
the  Hoosac  conglomerate  and  white  gneiss,  the  strong  possibility  that  at 
least  a  part  of  the  Greylock  column  was  contemporaneous  with  a  part  of  the 
Hoosac  column  had  presented  itself  to  me.  This  possibility  was  strength- 
ened when  we  had  correlated  the  quartzite  with  the  white  gneiss  and  con- 
glomerate beds  as  equivalents.  The  truth  of  this  hypothesis  could  be  tested 
only  by  finding  beds  showing  lateral  transition  to  bridge  the  narrow  belt 
between  the  Stockbridge  limestone  and  the  Hoosac  schist. 

In  the  progress  of  om-  survey  we  found,  at  various  points  between  the 
valley  and  the  mountain,  and  always  east  of  the  limestone,  outcrops  of  a 
peculiar  rotten  schist — quartz  and  mica  with  some  feldspar,  with  the  mica 
arranged  in  long  narr(jw  flakes  and  with  sufficient  calcite  to  show  the  cause 
of  the  decomposition.  The  occurrence  of  this  peculiar  calcareous  rock 
along  the  boundary  between  limestone  and  quartzite,  as  on  Tophet  creek 
and  below  the  albitic  schist  in  the  western  end  of  the  tunnel,  shows  that  it 
belongs  in  the  horizon  of  the  vertical  transition  between  the  quartzite  and 
the  limestone,  and  it  seems  to  represent  also  the  lateral  transition  zone  in 
this  horizon  Ijetween  the  Hoosac  and  Greylock  columns. 

East  of  North  Adams,  on  the  road  to  Briggsville,  the  river  cuts  longitu- 


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GENERAL  STEUGTURE  AND  CORRELATION.  15 

diually  through  an  anticline ;  a  few  huu tired  feet  west  of  the  river  there  is 
a  massive  anticline  of  marble  exposed  in  large  quarries  ;  the  eastern  end 
dips  toward  the  river,  but  a  sharp  anticlinal  fold,  slightly  overturned  to  the 
west,  brings  the  strata,  up  near  the  west  bank  of  the  stream,  in  interstrati- 
lied  beds  of  limestone  and  schist.  The  arcli  springs  over  the  river,  and  its 
easterly  dipping  limlj  forms  a  high  cliff  on  the  eastern  bank.  In  this  eastern 
limb  the  limestone  is  represented  by  calcareous  siliceous-micaceous  schists 
and  very  impure  limestones.  The  whole  arch  is  exposed  near  by,  in  a  cliff 
in  the  bend  of  the  river  (see  Fig.  4). 

This  is  the  most  eastern  exposure  of  limestone,  and  there  can  be  no 
doubt  that  we  are  here  in  the  zone  of  lateral  transition  between  the  condi- 
tions that  produced  in  the  same  horizon  the  Stockbridge  limestone  and  part 
of  the  Hoosac  schist.     Again,  along  the  north  base  of  the  Dalton  hills,  in 


Fig.  4 — Amiclinal  arch  across  Hoosic  river  between  North  Adams  and  Briggsville, 
ill  the  zoiie  of  lateral  transition  hetween  Stockbridge  limestone  and  Uoosac  scliist: 
a,  limestone  more  or  less  micaceous  and  siliceous;  6,  calcareous  and  siliceous  sithist 
witll  thin  layers  of  limestone;  an,  interstratified  siliceous  and  micaceous  Jimestonc, 
calcareous  quartzite  and  mica-schist;  66.  less  calcareous  garnetiferous  schist. 

Cheshire,  Mr.  Wolff  found  a  schist  consisting  of  calcite,  mica,  quartz  and 
simple  twinned  albite,  which,  from  its  position  and  nature,  vmdoubtedly 
represents  this  zone  of  lateral  transition  from  limestone  to  schist. 

If  the  reader  will  turn  to  Plate  ii  he  will  see  that  the  Stockbridge 
limestone  sends  a  broad  rectangular  bay  southeast  in  Cheshire  to  conform 
to  the  embayed  topography  of  the  Dalton- Windsor  hills.  In  the  middle  of 
this  embayment  he  will  observe  a  detached  area  of  Berkshire  schist  of  an 
irregular  sha[)e,  suggesting  a  long-eared  rabbit.  There  is  no  question  as  to 
the  continuity  of  the  schist  over  the  area  as  represented.  The  long  rabbit- 
ear-like  area  lies  upon  the  limestone  in  a  synclinal  trough.  The  structure 
of  this  area  is  not  simple ;  it  is  that  of  a  small  synclinorium,  the  axes  of  the 
north-south  running  folds  pitching  toward  the  center,  and  the  folds  at  the 
northern  end  being  more  or  less  overturned  to  the  west  in  conformity  with 


16  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

the  general  overfolding  of  Hoosac  mountaiu  and  the  Daltou-Wiudsor  hills. 
Tlie  limestone  proper  borders  the  whole  western  side  of  the  area  and  ex- 
tends well  into  the  bay  east  of  Cheshire.  On  the  east  side  it  also  extends 
visibly  down  from  the  north  for  some  distance,  but  it  then  disapjjears  under 
a  heavily  drift-covered  area.  Going  south  from  the  limestone  on  this  east 
side,  the  first  exposures  we  find  belong  to  a  continuous  belt  of  the  schists 
connecting  the  Cheshire  schist  area  with  the  tongue  of  schist  infolded  in 
the  Cambrian  white  gneiss  farther  east  at  the  base  of  Hoosac  mountain. 
There  is  neither  any  trace  of  the  limestone  nor  any  room  for  it. 

On  the  south  of  the  Cheshire  schist  area  the  Cambrian  quartzite  covers 
the  Dalton- Windsor  hills,  the  topography  of  which  is  formed  by  the  undu- 
lations and  intervening  sharp  folds  of  this  hard  mantle.  The  dip  of  the 
undulating  quartzite  beds  and  the  pitch  of  their  sharp  folds  are  both  toward 
the  center  of  the  Cheshire  schist  synclinorium. 

The  Cheshire  schist  hills  are  separated  from  the  higher  Dalton- Windsor 
quartzite  hills  by  a  narrow  valley,  which  curves  around  the  southern  end  of 
the  former  with  few  exposures.  But  at  one  point  quartzite  and  schist  are 
very  near  together,  and  it  is  evident  that  there  is  no  room:  for  the  limestone 
as  such.  In  this  valley  there  are  large  numbers  of  gr.eat  angular  blocks 
and  at  least  one  ledge  belonging  to  a  transitional  scldst  formation.  I 
repeat  here  L)r.  Wolff's  description  of  this  important  rock: 

It  resembles  a  micaceous  white  limestoue  fiUed  witli  little  dark  grains  or  imper- 
fect crystals  of  feldspar.  Under  the  miscroscope,  in  thin  section,  it  is  composed  of  a 
mass  of  calcite  grains,  with  here  and  there  single  grains  of  quartz,  or  an  aggregate  of 
several  grains,  plates  of  muscovite  and  often  of  chlorite  and  biotite,  and  large  por- 
phyritic  feldspar  grains  in  single  crystals  or  simple  twins,  very  rarely  showing  poly- 
synthetic  twinning.  These  feldspars  contain  inclusions  of  mica,  quartz,  iron  ore, 
rutile,  and  calcite.  and  are  in  every  way  identical  with  the  albites  of  the  albitic 
schists,  although  the  exact  species  of  plagioclase  has  not  been  determined.  The 
calcite  seems  to  play  the  part  which  the  quartz  does  in  the  schists:  it  sends  tongues 
into  the  feldspars  or  cuts  them  in  two,  and  gives  one  the  impression  by  its  inclusions  in 
the  feldspar,  and  its  occurrence  with  the  quartz  and  mica,  that  it  is  of  contempora- 
neous origin  with  the  feldspar,  mica,  and  quartz. 

This  schist  represents  the  landward  transition  of  the  Stockbridge  lime- 
stone into  the  Hoosac  albitic  schist.     Thus  the  Cheshire  schist  area  is  at  its 


GENERAL  STRUCTURE  AND  CORRELATION. 


17 


Fig.  5. — Ideal  section  east  of  Cheshire,  showing 
lateral  transition  of  limestone  to  Hoosac  schist;  S, 
Berkshire  schist;  i,  Stockbridge  limestone:  ^,  Lower 
Cambrian  qnartzite  of  Dalton- Windsor  liills;  Ci/,  cal- 
careous quartzite:  transition  quartzite  to  limestone; 
OS,  calcareous  feldspathic  scliist  in  lateral  transition 
from  Stockbridge  limestone  to  Hoosac  schist. 


northern  end  simply  the  Berkshire  schist  resting  upon  the  Stockbridge 
limestone,  while  as  we  go  southward  we  find  it  representing  not  <^nly  the 
Berkshire  schist,  but  also  the  whole  thickness  of  the  limestone  itself,  and  as 
we  go  eastward  we  find  through  continuous  exposures  its  connection  and 
identity  with  the  tongues  of  schist  infolded  in  the  Cambrian  quartzite 
gneiss  of  Hoosac  mountain. 

In  Fig.  5  I  have  attempted  to  represent,  in  a  somewhat  ideal  section, 
the  transition  from  limestone  to  schist  at  the  south  end  of  the  Cheshire  hill. 
The  transition  is  clearly  quite  abrupt, 
and  might  easily  occur  within  the  space 
represented  by  the  eroded  folded  arch 
between  the  limestone  and  the  infolded 
schist  along  the  west  base  of  Hoosac 
mountain.     See  c,  PI.  iii. 

The  western  end  of  the  Hoosac  tun- 
nel lies  in  the  belt  of  this  lateral  transi- 
tion of  the  Stockbridge  limestone  into  the 
Hoosac  schists;  but  it  is  now  completely  hidden  by  the  brick  arching  ren- 
dered necessary  by  the  decomposed  condition  of  the  material.  Indeed,  it 
acted  for  several  hundred  yards  from  the  portal  as  a  quicksand,  and  the 
tunneling  work  had  to  be  preceded  by  small  tunnels  incased  in  closely 
matched  planks,  so  fluid  was  the  decomposed  water- saturated  rock.  I  have 
attempted  to  represent  the  structural  facts  at  this  point  on  the  west  flank  of 
Hoosac  mountain  in  D,  PI.  iii. 

At  the  time  of  my  examination  of  the  tunnel,  in  186.5,  the  limestone 
was  exposed  in  open  cuts  and  tunnels — nearly  parallel  to  the  present  open 
cut — ^for  nearly  700  feet  east  and  west.  The  exposure  showed  in  this  dis- 
tance two  rather  flat  anticlines.  The  eastern  limb  of  the  easternmost  anti- 
cline dipped  east  and  was  for  a  short  distance  concealed  by  masonry.  East 
of  this  was  an  open  cut,  for  nearly  400  feet,  in  the  decomposed  rotten  schist, 
which  seemed  to  show  faintly  preserved  indications  of  an  easterly  dip. 
Just  east  of  the  middle  of  the  cut  a  less  altered  bed  showed  a  well-defined 
syncline  with  an  anticline  on  the  east  and  having  the  eastern  limb  of  the 
latter  exposed  in  the  heading  with  easterly  dipping  structure. 


MON  XXIIT- 


18  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

From  the  above  description  it  will  be  seen  that  the  actual  nature  of 
the  relation  of  the  limestone  to  the  rotten  schist  was  hidden.  But  just  west 
of  where  the  contact  should  be  I  found  the  limestone  conformably  overlain 
by  a  few  feet  of  Hoosac  schist.  Farther  east  is  a  small  shaft,  from  which 
was  hoisted  some  of  the  rock  excavated  between  the  western  headings  of 
the  "west"  shaft  and  the  open  cut;  this  rock  is  a  more  or  less  rotten  calca- 
reous feldspathic  mica-schist,  having  the  same  elongated  structure  parallel 
to  the  axes  of  the  folds  as  in  the  rotten  transition  schists  of  this  zone,  and 
marked  by  the  same  similarly  an-anged  long,  narrow  flakes  of  mica.  It 
recalls  in  structure,  also,  at  once,  the  calcareous  gneiss  associated  with  the 
limestone  on  its  eastern  border  near  South  Adams,  and  also  the  noncalca- 
reous  and  rather  less  feldspathic  mica-schist  of  the  "Buttress"  core.  I 
think  that,  taken  in  coimection  with  the  facts  observed  south  and  east  of 
Cheshire  hill,  we  have  in  this  rock  the  upward  transition  from  the  quartzite 
to  the  limestone  brought  to  the  tunnel  line  in  an  anticlinal  arch,  and  that 
we  have,  in  the  wholly  decomposed  material  of  the  former  open  cut,  the 
lateral  transition  from  the  rest  of  the  limestone  into  the  Hoosac  schist.  A 
few  hundred  feet,  from  east  to  west,  would  span  the  whole  lateral  passage 
from  limestone  to  Hoosac  schist.  This  transitional  calcareous  schist  decom- 
poses much  more  easily  than  the  limestone  and  is  therefore  more  rarely 
seen.  Nevertheless,  as  stated  above,  it  is  found  exactly  where  it  should 
occur  as  such  a  transitional  form,  not  only  in  the  western  end  of  the  great 
tunnel,  but  at  several  points  along  the  western  base  of  Hoosac  mountain 
above  the  quartzite  and  west  of  the  infolded  schists. 

While  the  rocks  of  the  zone  of  lateral  transition,  in  the  horizon  of  ver- 
tical transition  from  quartzite  to  limestone,  were  tolerably  hard,  they  suc- 
cumbed to  disintegrating  agents  much  quicker  than  the  quartzite  proper. 
But  the  rocks  of  the  zone  of  lateral  transition  between  the  limestone  and 
Hoosac  schist,  being  calcareous  schists,  were  adapted  to  the  most  rapid 
destruction,  and  we  therefore  find  them  only  where  the  conditions  for  their 
preservation  have  been  exceptional. 

From  Cheshire  hill  northward  this  zone  covered  anticlinal  folds  turned 
over  to  the  west,  which  have  been  to  a  great  extent  eroded  down  to  the 
harder  beds  towards  the  true  quartzite.     It  does  not  seem  improbable  that 


GENERAL  STEUCTUEE  AND  COEEELATION.  19 

the  zone  of  lateral  transition  of  limestone  to  Hoosac  schist  was  a  zone  of 
weakness  which  had  ranch  to  do  with  the  overfolding  along  the  west  base 
of  Hoosac  mountain.  These  anticlinal  axes  are  inclined  gently  to  the 
north.  About  a  mile  south  of  the  tunnel,  at  the  "Buttress,"  the  core  of  one 
is  visible  as  a  hard,  white  gneiss,  but  at  the  tunnel  line  it  has  sunken  to 
where  the  erosion  surface  cuts  the  beds  representing  the  lateral  transition 
of  limestone  to  schist,  where  they  mantle  around  the  pitching  anticline, 
and  before  they  disappear  under  the  younger  schist  beds  which  stretch 
out  from  the  mountain. 

While  the  equivalence  of  the  Greylock  column  with  a  large  part  of 
the  Hoosac  column  can  be  thus  asserted,  I  am  not  yet  in  a  position  to  make 
a  correlation  reaching  into  details.  It  is  not  possible  with  our  present  data 
to  subdivide  the  Hoosac  column  into  equivalents  of  the  two  schists  and  two 
limestone  horizons  of  Greylock.  There  is,  indeed,  in  the  eastei'u  half  of 
the  Hoosac  mountains  a  rather  sharply  defined  plane  of  division,  separating 
the  feldspathic  schist  on  the  west  from  the  practicall)^  nonfeldspathic  schists 
on  the  east,  and  these  latter  are  distinguished  further  by  the  fact  that  their 
quartz  is  distributed  in  thin,  even  layers,  instead  of  occupying  lenses,  as  in 
the  rocks  to  the  west.  This  plane  is  used  by  Prof  Emerson  as  the  base 
of  his  lower  hydromica-schist,  and  forms  an  impoi-tant  horizon  of  reference 
in  his  work  east  of  the  mountain.  The  thickness  of  the  albitic  schists 
between  this  plane  and  the  conglomerate  has  not  yet  been  determined, 
as  the  structure  is  masked  by  the  cleavage.  It  is  certainly  not  more  than 
5,600  feet,  and  probably  not  less  than  2,500  feet.  If  there  are  no  faults 
or  foldings,  it  is  probably  about  4,000  feet.  We  are  equally  ignorant  of 
the  real  thickness  of  the  Greylock  beds,  after  allowing  for  the  effect  of 
lateral  pi'essure  and  increasing  local  thickness.  But  it  is  quite  possible, 
if  not  probable,  that  these  nonfeldspathic  schists  belong  wholly  above  the 
Greylock  rocks.  In  the  study  of  Greylock  mountain  Mr.  Dale,  by  patient 
search  for  the  traces  of  the  original  stratification,  which  have  here  and  there 
escaped  the  general  obliteration  caused  by  cleavage,  has  been  able  to  work 
out  the  details  of  surface  structure  quite  closely,  and  to  obtain  a  general 
idea  at  least  as  to  the  maximum  thickness  of  the  two  limestones  and  two 
schists.     But  the  compressed  foldings  have  so  altered  the  thickness  of  the 


20  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

strata  that  it  is  impossible    to    give  the    real    vertical    dimensions.      His 
estimate  is: 

Greylock  schist 1, 500-2, 000 

Bellowspipe  Umestoue 600-    700 

Berkshire  schist 1, 000-2, 000 

Stockbridge  limestone 1, 200-1, 400 

These  are,  however,  based  on  measurements  of  beds  that  have  been 
subjected  to  strong  lateral  compression,  and,  as  Mr.  Dale  observes,  although 
the  aggregate  maximum  of  the  thickness  given  above  is  below  that  assigned 
to  the  Lower  Silurian  in  the  Appalachian  region,  it  is  probably  far  in  excess 
of  the  real  thickness,  which  maybe  considerably  below  the  maximum  above 
given. 

^  The  sediments  which  in  vast  thickness  form  the  substance  of  the  Grreen 
mO'Untain  system  have  been  subjected  to  intense  lateral  thrust,  which  has 
produced  numerous  folds.  These,  as  a  rule,  are  more  or  less  compressed 
and  overturned  to  the  west,  in  places  indeed  forced  over  until  the  axial 
plane  lies  almost  horizontally,  or  compensations  have  taken  place  through 
overfaulting.  The  sections  and  map  of  the  Hoosac-Grreylock  ret,ion  illus- 
trate the  structure  in  its  generality. 

From  these  it  will  be  seen  that  on  Hoosac  mountain  the  granitoid 
gneiss  and  the  overlying  conglomerate  gneiss-quartzite  and  albitic  schists 
have  been  folded  into  a  low  anticlinal  arch,  the  western  side  of  which  has 
been  forced  over  to  form  an  overfold  to  the  west. 

An  examination  of  the  longitudinal  sections  on  Plate  vi  accompanying 
Part  11  (Mr.  Wolff's  report)  shows  that  the  southern  end  of  this  arch  is  over- 
folded  in  the  same  manner,  but  to  the  south.  We  have  thus  the  remarkable 
occurrence  of  an  overturned  anticline  abruptly  turning  a  right  angle.  A 
glance  at  the  map  (Plate  ii)  will  show  that  this  is  repeated  by  the  next  over- 
folded  anticline  to  the  west,  which  bends  equally  abruptly  around  to  run 
eastward,  and  that  the  inverted  trough  between  these  anticlines  is  still 
marked  by  the  infolded  band  of  schist.  Groing  from  this  southward,  Ave 
come  immediately  upon  another  east  and  west  trough  of  schist,  also  over- 
turned to  the  south.  Still  further  southwest,  we  find  along  the  northern 
part    of  the  Dalton- Windsor  hills  the  quartzite  gneiss  beds  thrown  into 


GENERAL  STEUOrUEE  AND  COREELATION.  21 

overfolds,  but  witli  the  axes  striking  northwest  to  southeast ;  while  still 
farther  westward  they  are  overfolded  to  the  west,  but  with  the  axes  in  the 
normal  position  of  the  Grreen  mountain  folds — nearly  north  and  south. 

Looking  at  the  map  and  sections  of  Grreylock,  Pis.  i,  xviii,  xxiii,  we  find 
a  great  basin-bottomed  mass,  thrown  into  numerous  more  or  less  overturned 
folds,  with  axes  in  the  normal  Green  mountain  position,  and  inclined  from 
each  end  toward  the  middle.  Again,  if  we  look  at  the  eastern  border  of  the 
map,  we  find  in  the  observed  strikes  and  dips  of  the  conglomerate  gneiss  and 
schist  east  of  the  granitoid,  no  trace  of  a  departure  from  the  general  Green 
mountain  direction. 

This  local  modification  in  the  structure  of  Hoosac  mountain  must  be 
due  to  some  local  cause,  which  I  think  must  be  sought  in  the  pre-Cambrian 
topography.  The  Greylock  basin  of  sediment  was  guarded  on  the  north 
by  the  large  mass  of  granitoid  gneiss  of  Clarksburg  mountain,  and  on  the 
south  by  the  great  body  of  pre-Cambrian  rocks  which  are  now  masked  by 
the  Dalton  and  Windsor  quartzite.  I  imagine  that  the  lateral  thrust  to 
which  the  foldings  are  due 'met  with  greater  resistance  opposite  these  mtire 
rigid  granitic  masses  than  in  the  interval,  and  that  the  abnormal  overfoldings 
to  the  south,  described  above,  are  the  result  of  compensatory  movement. 
The  Hoosac  mountain  cross  sections  show  a  much  more  marked  overturn 
than  is  observed  to  either  the  east  or  west  of  it.  The  axial  plane  of  the 
principal  overturned  fold  on  the  west  side  of  the  mountain  lies  very  flat. 
We  may  suppose  the  greater  rigidity  of  the  granitoid  gneiss '  to  have 
caused  it  to  yield  as  a  unit  to  the  contracting  force.  Only  its  relatively 
nari'ow  top  participated  in  the  actual  folding  and  was  carried  over  to  form, 
with  the  leeward,  protected  beds,  a  flat-lying,  compressed  syncline. 

A  similar  overturn,  though  not  so  flat,  was  observed  by  us  on  Sumner 
mountain,  in  Pownal,  on  the  west  of  the  Clarksburg  mass  of  granitoid 
gneiss.  Section  a  on  Plate  iii  was  made  by  Mr.  B.  T.  Putnam.  -  I  have 
added  my  interjjretation  in  dotted  lines.  This  outlier  is  separated  from 
Clarksburg  mountain  by  Broad  brook,  this  interval  being  occupied  by 
the  quartzite.  The  large  Clarksburg  mass  of  granitoid  gneiss  remained 
a  dome  mantled  by  the  Cambrian  quartzite,  and  showing  the  effect  of  the 
folding  force  only  in  the  induced  lamination   common  to  itself  and  the 


22  •    GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

quartzite,  while  in  the  smaller  mountain  to  the  west,  which  has  a  grani- 
toid gneiss  core,  this  core  is  pushed  up  in  the  form  of  an  overturned  anti- 
cline upon  which  the  quartzite  lies,  in  normal  position  on  the  east,  while  on 
the  west  the  granitoid  is  underlain,  in  inverted  order,  by  the  quartzite  and 
the  limestone. 

A  careful  study  of  the  western  flank  of  Hoosac  mountain  shows  that 
its  structure  is  not  that  of  a  simple,  great,  overtm-ned  fold.  It  consists  of  a 
series  of  parallel,  crumpled  folds,  one  or  more  of  which  have  a  greater  depth 
than  the  others.  All  of  them  are  overfolded,  with  their  axial  planes  dip- 
ping eastward  and  with  their  axes  pitching  about  10°  northward.  The 
average  chord-plane  of  these  folds  dips  westward  15°  to  20°,  forming  thus, 
as  a  whole,  a  comparatively  flat,  though  much  crumpled,  western  limb  of 


Fig.  6.— Diagram  of  structiu'e,  summit  of  the  Buttress,  ou  west  flank  of  Hoosac 
mountain,  about  one  mile  south  of  Hoosac  tunnel,    a,  Buttress  rock,  upper  part  .» 

of  Cambriau  white  gneiss ;  b,  Hoosac  schist.    The  exposure  at  the  east  end  is  part 
of  the  long  trough  infolded  along  the  whole  front  of  Hoosac  mountain. 

the  main  Green  mountain  anticlinal  arch.  This  structure  is  shown  in  nu- 
merous preserved  fold-cores,  and  is  illustrated  in  the  section  through  the 
"Buttress"  (Plate  in,  c)  and  in  the  annexed  diagram  of  the  summit  of  the 
same  hill  (Fig.  6).  The  "  Buttress"— a  high  hill  on  the  flank  of  the  mountain 
about  one  mile  south  of  the  tunnel— is  the  southerly  extension  of  one  of  the 
larger  of  these  crumples,  where  the  axis  in  rising  to  the  south  brings  up  the 
harder  core  of  Cambrian  white  gneiss.  The  structure  is  marked  both  by  the 
preserved  fold-core  at  a,  just  west  of  the  summit  (Fig.  6),  and  by  the  small 
infolded  troughs  of  younger  schist  at  b  on  the  summit  and  h  on  the  western 
flank.  Further  north,  as  at  the  tunnel  line,  where  nearly  the  whole  flank  of 
the  mountain  is  covered  by  the  schist,  the  crumpling  is  much  greater,  as 
one  would  expect  in  this  material,  and  is  marked  by  the  crumpled  layers  of 
quartz  (Fig.  7).  "  Toward  the  south  end  of  the  mountain,  near  where  the 


GENERAL  STEUCTUEE  AND  COEEELATION. 


23 


great  schist  trough  is  seen  on  the  map  to  turn  sharply  to  the  east,  the  evidence 
of  this  same  structure  is  preserved  in  several  minor  iufoldings  of  schist. 

In  the  tunnel  the  rotten  rock  of  the  old  open  cut,  and  that  which  I 
have  described  as  the  Buttress-core  rock  and  as  forming  below  it  the 
upward  transition  from  quartzite  horizon  to  limestone  horizon,  are  con- 
cealed by  masonry.  But  from  a  point  several  hundred  feet  west  of  the 
"west"  shaft  we  find  the  Hoosac  albitic  schist,  which  extends  some  1,400 
or  1,500  feet  fui-ther  east  till  we  reach  its  contact  with  the  underlying  con- 
glomerate-white-gneiss (See  PI.  Ill,  d).  This  last-mentioned  rock  extends 
some  2,000  feet  farther  east  to  its  contact  with  the  pre-Cambrian  coarse 
crystalline  gneiss  of  the  Hoosac  core.     On  both  its  eastern  and  western  sides 


w 


Fig.  7 Crumpled  structure  in  the  Hoosac  schist  above  the  "  west  shaft" 

on  Hoosac  mountain,    a,  cleavage  foliation ;  b,  stratification  lines  marked  by 
crumpled  quartz  layers. 

the  contact  planes  show  that  the  Cambrian  white  gneiss  is  overturned  in  a 
flat-lying  anticline.  Leaving,  now,  the  tunnel  and  climbing  to  the  opening 
of  the  "west"  shaft  on  the  flank  of  the  mountain  we  find  that  the  upper 
part  of  the  shaft  is  in  the  Buttress-core  rock — quartzite-limestoue  transi- 
tion rock — and  that  the  same  formation  crops  out  upon  the  mountain  until 
we  reach  the  Hoosac  schists,  several  hundred  feet  higher  up.  Climbing 
above  this  point  we  find  the  Hoosac  schists,  with  evidence  that  they  occupy 
an  inverted  syncline.  Fig.  7  shows  the  structure  at  this  point  on  a  small 
scale.  Above  this  the  dips  observed  on  both  sides  of  the  summit  show  that 
the  crest  is  a  simple  open  syncline. 

The  presence  of  the  Buttress-core  rock  at  the  top  of  the  "west"  shaft 
and  its  projection  so  far  westward  Qver  the  Hoosac  schist  of  the  tunnel 


24  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

below  can  be  explained  only  by  introducing  an  overthi'ust  fault  or  by  sup- 
posing that  the  inverted  anticline  was  pushed  out  thus  far  without  rupture. 
The  former  explanation  seems  the  more  likely  one  and  accords  better  with 
the  thickness  of  the  Cambrian  gneiss  and  the  dips  in  the  schist  observed  in 
the  tunnel.  The  bed  of  white  gneiss— 600  to  800  feet  thick— when  ex- 
posed to  the  great  thrust  which  overfolded  the  Hoosac  rocks,  would,  it 
seems,  be  less  able  to  adapt  itself  by  minor  foldings  than  the  more  readily 
yielding  schist,  and  would  be  more  likely  to  find  its  compensation  in  a 
rupture  and  an  overthrust  fault. 

At  the  tunnel  line  the  axes  of  the  folds  are  still  pitching  to  the  north. 
Immediately  north  of  the  limestone  is  a  mass  of  folded  Hoosac  schist,  under 
which  the  limestone  is  earned  by  the  pitch  of  its  folds  and  which  is  seen  at 
several  points  to  be  younger  than  the  limestone.  The  zone  of  lateral  tran- 
sition is  also  Qan-ied  under  this  hill,  and  this  fact  explains  the  peculiar  areal 
geology  of  this  part  of  the  map  (PI.  i)  on  which  the  color  for  the  Stock- 
bridge  limestone  extends  along  the  west  side  of  the  schist  hill,  that  for  the 
Vermont  formation  along  the  east  side.  The  obscurity  disappears  on  PI.  ii, 
where  I  have  separated  these  transitional  rocks  from  the  quartzite  and  given 
to  them  and  to  the  lower  part  of  the  limestone  a  separate  representation  as 
Cambrian. 

It  is  not  easy  to  determine  the  extent  to  which  overthrust  faulting  has 
entered  into  the  building  of  the  Grreen  mountain  range  in  northwestern  Mas- 
sachusetts. Along  the  eastern  side  of  the  pre-Cambrian  core  of  Hoosac 
mountain  the  movement  flattened  the  coarse  pebbles  of  the  conglomerate 
and  granulated  their  quartz  and  large  feldspars  to  the  point  of  obliteration. 
But  the  great  Cambrian  conglomerate-gneiss  bed  as  it  curves  around  the 
core  shows  no  break  due  to  faulting.  It  is  not  until  we  come  to  the  west 
side  of  the  pre-Cambrian  gneiss-core  that  we  find  evidence  of  a  rupture  in 
the  flat  fold,  where  the  hard  Cambrian  white  gneiss  has  been  pushed  along 
an  overthrust  fault  ont(i  the  younger  schists  as  far  as  the  west  shaft.  Here 
it  seems, probable  that  the  rupture  was  favored  by  the  fact  that  the  troughs 
of  the  folds,  both  above  and  below  the  middle  limb,  were  on  the  lee  side 
of  the  less  yielding  pre-Cambrian  core,  as  will  be  seen  from  the  section 
(PI  III,  u).     Now  this  is  the  same  fold  that  incloses  the  trough  of  schist  all 


GENERAL  STEUCTUKE  AND  COEEELATION.  25 

along  the  west  side  and  south  end  of  the  mountain,  and  it  is  not  impossible 
that  it  may  be  accompanied  there,  as  here,  by  the  same  ruptvire.  If  this  is 
so,  then  the  position  of  this  overthrust  plane  would  lie  above  and  to  the  east 
of  the  schist  trough  shown  on  the  Buttress  (PI.  in,  c,  d). 

Having  sketched  thus  briefly  the  general  relation  of  the  crystalline 
schists  of  the  main  ridge  of  the  Green  mountains  to  the  fossiliferous  rocks 
lying  to  the  west,  let  us  now  return  to  the  main  ridge. 

We  have  seen  that  the  Cambrian  white  gneiss  rests  with  a  time  break  on 
the  coarse  granitoid  gneiss  In  places  on  Clarksburg  mountain  we  find  the 
micaceous  quartzite  more  or  less  conglomeratic  at  the  base,  resting  on  the 
gi'anitoid  gneiss,  the  two  rocks  sharply  distinct.  In  others,  as  on  Hoosac 
mountain,  a  conglomerate  rests  on  the  granitoid  gneiss  with  sharp  definition. 
But  this  simplicity  is  not  always  present,  especially  at  the  meeting  of  the 
white  and  granitoid  gneisses.  In  general  there  intervenes  between  the 
well-defined  coarse  gneiss  and  the  well-marked  white  gneiss  a  zone  of  beds 
of  luore  or  less  coarse  gneiss,  often  alternating  with  finer  grained  biotite 
schists.  It  is  not  easy  in  such  places  to  draw  the  line  between  the  Cam- 
brian and  pre-Cambrian  formations,  though,  as  I  will  show  further  on,  in 
some  instances  there  is  good  reason  to  draw  the  line  at  the  base  of  the 
transitional  beds  where  these  show  alternating  strata  of  varying  character. 
One  thing  appears  certain  :  the  dynamic  action  which  has  folded  these  rocks 
has  impressed  upon  them  not  only  their  cleavage  and  plication,  but  also  the 
I'emarkable  simulation  of  conformity  in  bedding  and  of  vertical  transition. 

The  pre-Cambriau  core  of  the  Grreen  mountains  reappears  at  frequent 
points  along  the  range.  In  places  it  forms  almost  island-like  masses  of  old, 
hard  gneisses  surrounded  by  the  Cambrian  quartzites  and  allied  rocks,  as 
in  the  northwestern  corner  of  Connecticut.  In  others,  as  on  Hoosac  and 
Clarksburg  mountains,  it  appears  as  limited,  oval,  dome-like  areas  of  granitoid 
gneiss.  Again,  as  in  Chittenden,  Vermont,  it  consists  of  a  long,  narrow 
line  of  coarse  gneiss,  at  eroded  points  in  the  backbone  of  the  range. 
Finally,  as  between  Clarendon  and  Ludlow,  in  Vermont,  where  the  height 
of  the  range  has  been  cut  down  by  the  removal  of  the  younger  rocks,  the 
core  of  the  folded  range  shows  itself  in  a  variety  of  old  granitic  and 
gneissoid  rocks,  cut  by  intrusives  and  with  extremely  irregular  structure 


26  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

We  have  done  but  little  work  towards  the  study  of  this  old  core.  A 
valuable  clew  was  found  by  Prof.  Emerson  in  what  he  considers  to  be  a 
threefold  division  of  the  pre-Cambrian  iu  southern  Berkshire,  where, 
according  to  his  observations,  chondroditic  limestone  separates  a  coarse, 
blue  quartz  gneiss — possibly  the  Stamford  granitoid — from  a  still  older 
gneiss. 

The  massive  granitoid  gneiss  which  forms  the  core  on  Hoosac  and 
Clarksburg  mountains  is  in  places  separated  from  the  overlying  Cambrian 
quartzite  gneiss  series  by  beds  of  coarse,  light-colored  gneisses,  which  have 
interbedded  layers  of  finer  grain  and  darker  color  from  the  greater  propor- 
tion of  biotite.  These  "transitional  coarse  gneisses"  between  the  granitoid 
and  white  gneisses  are  probably,  to  a  great  extent  at  least,  Cambrian. 
They  are  detrital,  containing  pebbles  in  places,  as  in  the  tunnel.  Their 
coarse  feldspar  is  identical  with  that  of  the  granitoid  gneiss,  except  that  in 
this  transitional  zone  it  is  white,  while  in  the  granitoid  it  is  reddish.  While 
the  granitoid  gneiss  is  preeminently  a  massive  rock,  this  "transitional"  zone 
is  bedded  and  contains  micaceous  layers.  On  the  east  side  of  the  granitoid 
area  on  the  surface  of  Hoosac  mountain  it  occupies  the  place  of  the  quartz- 
ite-white-gneiss-conglomerate  and  is  overlaid  conformably  (as  seen  at  the 
contact)  by  the  albite-schists.  The  granitoid  gneiss  was  probably  much 
disintegrated  at  the  time  of  the  Cambrian  transgression,  and  in  the  differ- 
ent conditions  of  character  of  disintegrated  material  and  of  breaching  and 
sedimentation  lies,  perhaps,  to  a  considerable  extent,  the  explanation  of 
the  fact  that  this  horizon  is  here  quartzite  and  there  gneiss,  and  presents 
itself  under  a  great  variety  of  aspects,  due  to  alternating  layers  with  vary- 
ing proportions  of  quartz,  feldspar,  and  mica.  But  in  the  field  it  is  often 
very  difficult  to  distinguish,  in  the  absence  of  true  pebbles  and  of  alter- 
nating sediments,  between  the  redeposited  detritus  of  disintegration,  which 
has  been  subjected  to  the  action  of  chemical  and  dynamic  metamorphism, 
on  the  one  hand,  and  beds  which,  simulating  these,  have  been  produced 
by  the  action  of  these  same  metamorphic  agencies  directly  upon  the  older 
gneisses,  granites,  or  basic  eruptives. 

I  imagine  that  the  Cambrian  transgression  found  an  Archean  elevation 
forming  the  western  border  of  an  Archean  dry  region.     To  the  west  of  this 


GENERAL  STKUCTURE  AND  CORllELATION.  27 

lay  the  great  Paleozoic  ocean  of  America.  I  imagine,  also,  that  the  rocks 
of  this  dry  area  had  become  disintegrated  to  a  greater  or  less  depth  and 
that  the  products  of  this  action  varied  from  kaolin  and  quartz  at  the  surface 
to  semikaolinized  material  with  fresh  cores  at  depths.  The  depth  of  this 
action  would  vary  according  to  varying  lithologic  and  topographic  condi- 
tions, as  I  have  shown  elsewhere.' 

While  the  abrasion  of  the  deeply  disintegrated  rock  was  progressing 
along  the  advancing  beach  line  the  detritus  of  sand  and  pebbles  arising 
from  this  disintegrated  material  was  deposited  with  varying  proportions  of 
its  constituents  in  a  continuous  sheet  in  progressive  "transgression"  over 
the  previously -dry  land;^  for  I  think  the  evidence  offered  by  the  erosion  of 
the  Stamford  dike  is  sufficient  to  show  that  the  region  owed  its  absence  of 
older  sediments  to  its  having  been  an  area  of  dry  land  instead  of  an  "abyssal" 
area. 

During  the  progress  of  this  removal  and  deposition  of  ready-prepared 
material  there  would  be  places  where  the  underlying  unaltered  rock  would 
be  washed  clean  and  re-covered  with  sand  and  gravel.  There  would  be 
others  where  the  material  removed  from  the  disintegrated  mass  would  be 
derived  from  the  zone  of  semikaolinized  fragmentary  disintegration,  and 
places  where  this  material  would  be  deposited  without  having  been  much 
rolled  and  in  beds  alternating  with  finer  material.  And  again  there  would 
be  places  where  the  disintegration  was  deeper — in  basins  as  it  were — and 
where  this  material  escaped  removal  and  was  covered  by  the  sedimentary 
beds.  The  recognition  of  these  premises  would,  it  seems  to  me,  aid  in  the 
explanation  of  many  of  the  difficult  points  observed  in  the  field. 

Take,  for  instance,  the  schistose  lamination  of  the  Stamford  gneiss  on 
Clarksburg  mountain,  where  this  structure  is  most  highly  marked  near  the 
contact  with  the  overlying  quartzite.  The  lamination  is  parallel  in  both  rocks. 
The  quartzite  here  bends  around  the  mountain  and  is  highly  crinkled,  this 
structure  being  defined  by  the  micaceous  constituent,  and  for  some  distance 

'  Secular  rock  disintegration,  etc.  Am.  Jour.  Sci.,  vol.  17,  1879,  pp.  133-144.  Also  the  applica- 
tion and  extension  of  the  ideas  advanced  in  that  paper.     F.  von  Richthofen:  China,  vol.  2,  p.  758. 

'^  F.  von  Richthofen  has  called  attention  to  the  fact  that  toe  little  importance  has  been  attached 
by  geologists  as  a  rule  to  the  breaching  and  abrading  action  of  the  ocean  when  the  beach  line  is 
advancing  landward.     China,  vol.  2,  p.  768. 


28  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

inward  the  same  structm-e  is  similarly  defined  in  the  granitoid  gneiss  and 
is  perfectly  conformable  in  the  two  rocks,  although  we  have  here,  in  the 
conglomeratic  character  of  the  base  of  the  quartzite  and  in  the  pre-Cambrian 
erosion  of  the  Stamford  dike,  evidence  of  a  time-break.  If  we  imagine  the 
granitoid  gneiss  to  have  been  deeply  disintegrated  and  to  have  been  abraded 
only  to  the  semidisintegrated  zone,  or  even  to  the  lower  zone  in  which 
only  the  integrity  of  the  micaceous  element  had  been  attacked,  then  the 
material  of  this  zone  would  have  presented  itself  to  the  force  that  produced 
the  crinkling  and  lamination  in  much  the  same  physical  condition  as  the 
sand  and  pebbles  of  the  quai-tzite. 

Again,  take  the  coarse  gneisses  with  blue  quartz  which  occur  at  many 
points  along  the  core.  Mr.  Wolff  finds  them  to  contain  the  same  feldspar 
with  the  same  inclusions  as  that  of  the  granitoid  gneiss,  except  that  they  are 
light  colored,  while  those  of  the  granitoid  are  reddisli,  and  thev  have  fre- 
quently the  same  blue  quartz.  But  they  are  bedded  and  have  alternating 
layers  of  finer  schists,  and  a2)2jear  as  transitions  conformable  to  the  under- 
lying granitoid  and  overlying  white  gneiss  or  other  equivalents  of  the  Cam- 
brian quartzite.  The  granitoid  gneiss  consists  of  large  crystals  of  feldspar — 
perhaps  averaging  one  by  three-quarters  by  one-third  inch  in  size — and 
flattened  lenses  of  blue  quartz  and  thin,  irregular  layers  of  mica.  I  imagine 
that  these  materials,  taken  from  the  zone  of  semidisintegration  and  quickly 
deposited,  would,  in  their  new  arrangement,  produce  our  "transitional 
coarse  gneisses,"  while  the  material  of  the  upper  zone  of  complete  decay 
would  furnish  the  sand  and  clay  for  the  quartzite  and  finer  sediments. 

If  this  reasoning  be  correct,  we  should  in  many  instances  include  in 
the  Cambrian  quartzite  series  the  coarse,  more  thinly  bedded  gneisses,  with 
then-  iuterbedded,  finer  grained  schists.  But  in  the  present  state  of  our 
knowledge  of  the  Grreen  mountains  the  granitoid  gneiss  appears  to  be  only 
one  of  the  constituents  of  the  old  core,  and  perhaps  a  subordinate  one. 
From  our  recent  work  in  Vermont  it  seems  that  the  pre-Cambrian  area  will 
be  found  to  contain  a  variety  of  granites,  gneisses,  and  schists,  as  well  as 
basic  rocks,  which  will  need  to  be  studied  in  connection  with  the  rocks  of 
both  the  New  York  highlands  and  the  Adirondacks.  It  therefore  remains 
to  be  discovered  whether  the  old  core  contains  any  rocks  of  the  periods  be- 


GENERAL  STRUCTURE  AND  CORRELATION.  29 

tween  the  Archean  (Laurentiau)  and  Cambrian.  Thus  fai*  only  some  ob- 
servations that  will  serve  as  clews  have  been  made  in  this  direction/  One 
apparently  negative  piece  of  evidence  may  be  seen  at  the  place  where  the 
Archean  rocks  of  the  New  York  highlands  suddenly  end  near  Poughquag, 
Dutchess  county,  New  York.  Here  the  highlands  end  in  a  promontory 
of  nearly  vertical  beds  of  old  gneisses,  against  which  the  Cambrian  qtiartz- 
ite  lies  with  a  very  flat  dip. 

Toward  the  correlation  of  the  Green  mountain  rocks  with  the  fossilif- 
erous  strata  of  New  York,  the  paleontologists  have  given  us  some  facts. 
Mr.,  Walcott's  discovery  of  Olenellus  casts  in  the  quartzite  of  Clarksburg 
mountain,  about  100  feet  above  its  base,  caused  him  to  assign  that  rock  to 
the  Lower  Cambrian.  The  many  findings  of  Lower  Silurian  fossils  in  the 
limestone  of  Vermont  have  shown  that  limestone  to  include  Calciferous, 
Chazy,  and  Trenton  horizons,  and  it  is  inferred  that,  since  the  limestone  is 
Trenton  and  is  capped  by  schists,  the  latter  are  of  the  age  of  the  Utica  and 
Hudson  River  slates. 

I  have  shown  above  that  the  white  gneisses  and  conglomerates  of 
Hoosac  mountain  are  the  equivalents  of  the  Cambrian  quai'tzite  and  that 
the  albitic  schists  of  Hoosac  mountain  represent  in  time  both  the  limestone 
and  schists  of  the  valley,  and  therefore  range  from  the  Cambrian  into  or 
through  the  Hudson  River. 

It  seems  probable  that  the  limestone  must  reach  down  well  into  the 
Cambrian  and  that  all  of  the  Cambrian  that  is  not  represented  by  the 
quartzite  must,  in  the  valley,  be  included  in  the  lower  part  of  the  limestone 
and  its  downward  transition  beds;^  while  on  the  mountain  it  must  be  in- 
cluded in  the  lower  beds  of  the  albite  schists. 

We  have  yet  to  discover  whether  the  nonfeldspathic  schist  of  the 
eastern  portal  of  the  tunnel  (Rowe  schist)  represents  Hudson  River,  or, 
Ijerhaps,  Medina  time.  Geologically  above  the  nonfeldspathic  schists  of 
the  eastern  portal,  and  coming  in  successively  to  the  east  to  build  up  the 
old  plateau  region  that  forms  properly  the  eastern  belt  of  the  Green  moun- 

'  Since  this  was  written  we  have  fonnd  Algonkiau  schists  at  several  points  along  tlie  Green  moun- 
tains. 

-  This  has  been  confirmed  by  recent  discoveries  of  Cambrian  fossils  in  the  lower  part  of  tlie  lime- 
stone near  Rutland  and  Clarendon,  Vermont,  by  Messrs.  Foerste,  Wolft',  and  Dale. 


30  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

tain  system  as  far  as  the  Connecticut  valley,  there  is  a  series  of  schists 
having  a  great  aggregate  thickness.  Prof  Emerson,  to  whose  report  the 
reader  is  referred  for  the  descriptions  and  for  the  views  of  our  predecessors, 
has  been  able  to  divide  these  schists  into  several  distinct  formations  with 
persistently  defined  characters  and  boundaries.  Above  the  nonfeldspathic 
Rowe  schists  comes  a  horizon  of  hornblende  schist  (Chester  amphibolite) 
often  with  serpentine,  varying  from  a  feather  edge  to  3,000  feet  in  thick- 
ness, overlain  by  over  9,000  feet  of  "upper  hydromica-schist"  (Plainfield 
schist).  This  in  turn  is  overlain  by  the  "Calciferous  mica-schist"  of  the 
Vermont  survey  (Conway  schist),  which  obtained  its  former  name  from  the 
presence  of  occasional  large  lenses  of  more  or  less  biotitic  limestone,  which 
latter  has  beds  of  hornblende-feldspar-schist  in  places  along  its  bottom  and 
top.  Above  this  again  is  the  heavy  bed  of  Leyden  argillite,  with  inter- 
calated quartz-schist.  Next  above  and  unconformably  supeq^osed  are  the 
representatives  of  the  Devonian.  The  age  of  these  different  fonnations 
still  remains  uncertain,  though  at  least  the  Leyden  argillite  and  the  Conway 
schist  ("Calciferous  mica-schist")  are  supposed  by  Prof  Emerson  to  belong 
to  the  Upper  Silurian. 

While  the  Green  mountain  system  includes  the  whole  region  between 
the  Connecticut  and  the  Hudson,  its  characteristic  features  consist,  as  we 
have  seen,  of  the  central  anticlinal  ridge  of  the  Green  mountains  proper 
on  the  east,  the  synclinal  range  of  the  Taconic  mountains  on  the  west,  and 
a  succession  of  high,  synclinal,  island-like  masses  rising  from  the  intermedi- 
ate valley.  The  results  of  the  survey  in  northwestern  Massachusetts  lead 
to  the  supposition  that  the  central  or  main  ridge  was  in  pre-Cambrian  time 
outlined  as  a  mountain  range  of  highly  crystalline  rocks  on  the  western 
border  of  an  area  of  dry  land.  During  long  exposure  to  the  action  of 
atmospheric  agencies  and  of  the  products  of  vegetable  decay,  the  rocks  of 
this  region  had  become  decomposed  at  the  surface  and  disintegrated  at 
depths. 

The  breaching  action  along  the  advancing  shore  line  of  the  Cambrian  sea 
found  ready  prepared  the  materials  which  the  water  assorted  and  distributed 
to  form  the  great  sheet  of  Cambrian  rocks.  While  these  deposits  of  detritus 
were  accumulating  over  the  shallow  areas,  the  mateiials  for  the  future  lime- 
stone were  gathering  offshore  to  the   west.      As  the  positive  movement 


GENERAL  STRUOTUEE  AND  CORRELATION. 


3] 


deepened  the  water  shoreward,  the  calcareous  materials  accumulated  above 
the  earlier  detrital  beds,  so  that  we  may  imagine  that,  while  the  later 
beds  of  the  Cambrian  were  being  made  of  sand  and  gravel  in  shallow 
water,  the  lower  beds  of  the  great  limestone  formation  were  being  deposited 
offshore.  Later,  with  a  change  of  some  kind  in  the  conditions,  there  came 
the  deposit  of  finer  material  over  the  previously  shallow  region,  while  the 
accumulation  of  limestone,  with  Lower  Silurian  organisms,  still  continued 
offshore.  Still  later,  by  another  change  in  the  conditions,  the  deposit  of 
finer  detrital  material  extended  far  to  seaward,  covering  everywhere  the 
limestone  accumulations. 


u 


Stanibrrl  TransvUonat 
Gneiss     Gn^ss 


FiQ.  8.— Map  showing  the  varying  character  of  the  Cambrian  rocks  in  con- 
tact with  the  pre-Cambrian  granitoid  gneiss  mass  on  Hoosac  mountain. 

As  we  are  not  yet  able  to  say  to  what  depth  into  the  Cambrian  the  lime- 
stone may  extend  in  the  Hoosac  valley,  so,  also,  we  are  unable  to  say  to 
what  extent  the  lower  beds  of  schists  on  Hoosac  mountain  may  represent 
Cambrian  time. 

Mr.  Wolff  has  shown  that  the  Cambrian  quartzite  horizon,  which  is  a 
true  conglomerate  on  the  top  of  the  arch  at  the  north  end  of  the  granitoid 
gneiss  area,  consists  on  the  eastern  and  easterly  dipping  limb  of  coarse 
gneisses,  showing  only  occasional  pebbles,  as  in  the  tunnel,  while  on  the 
western  and  crumpled  limb  it  is  represented  by  finer-grained  white  gneiss. 
These  relations  are  shown  in  Fig.  8.  We  may  suppose  an  island  of 
coarse  granitoid  gneiss  with  a  disintegrated  mantle,  and  imagine  this  latter 
to  have  been  abraded  down  to  its  less  disintegrated  zone,  and  the  resulting 


32  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

coarser  material  to  have  beeu  laid  down,  during  the  positive  movement,  over 
the  gneiss  area.  In  the  subsequent  folding  I  imagine  that  the  rigidity  of 
the  unaltered  granitoid  mass  offered  far  greater  resistance  to  the  folding 
than  any  of  the  superposed  material,  and  that,  as  a  result  of  this  resisting, 
inverted  wedge,  the  material  of  the  eastern  limb  was  subjected  to  the  slip- 
ping or  shearing  movement  producing  the  coarse  laminated  structure  of 
these  gneissoid  rocks,  while  the  similar  material  on  the  west  limb,  having 
a  more  rigid  base  which  yielded  less  readilv  to  overfolding,  was  forced  into 
minor  overfolded  crumples  and  crushed  into  a  finer  grain.  Beneath  the 
gneisses  remade  out  of  the  conglomerate  by  dynamic  action  during  the 
folding,  there  would  be  formed  more  or  less  similar  transitional  rocks 
through  the  action  of  the  same  dynamic  processes  upon  the  semidisinte- 
grated  surface  of  the  older  rock.  This  is  what  is  found  at  many  points 
along  this  contact  in  Hoosac  mountain. 

From  what  has  just  been  said  it  is  evident  that  the  high  degree  of 
metamorphism  of  the  Paleozoic  rocks  is  intimately  connected  with  the 
folding.  It  is  also  a  salient  fact  that,  while  the  schists  and  limestone  are 
wholly  recrystallized  throughout  the  whole  folded  area  beginning  west  of 
the  Taconic  range,  the  change  of  the  underlying  Cambrian  quartzite  to 
a  crystalline  rock — a  white  gneiss — does  not  begin  until,  in  going  east,  Ave 
reach  the  central,  main  range.  In  this  sense  the  metamorphism  of  the 
schists  is  regional ;  that  of  the  quartzite  has  the  apjDearance  of  being  local. 

Both  the  quartzite  and  the  ovei'lying  schists  contain  tourmaline,  crys- 
tallized in  situ,  and  frequent  lenses  or  faulted  veins  of  quartz,  feldspar,  and 
tourmaline.  The  schists  contain  in  places  needles  of  rutile.  As  we  follow 
the  quartzite  in  its  transition  to  white  gneiss  we  find  here  and  there  peg- 
matite veins,  more  often  near  its  contact  with  the  core  of  older  gneiss. 

If  we  could  go  back  to  the  original  character  of  the  sediments  we  would 
find  west  of  the  western  flank  of  Hoosac  mountain  a  column  of  fine  sedi- 
ments, probably  argillaceous,  with,  in  places,  calcareous  bands,  resting  on  a 
thousand  feet  or  more  of  limestone,  and  this  on  six  or  eight  hundred  feet 
of  Lower  Cambrian  grit — here  a  quartz  sandstone.  On  the  eastern  side  of 
the  western  flank  of  Hoosac  mountain  we  would  find  many  thousand  feet 
of  the  same  fine  sediments  resting  on,  and  passing  downward  into  the 
Cambrian  grit — here  a  coarse  conglomerate  abounding-  in  detrital  feldspar 


GENERAL  STRUCTURE  AND  CORRELATION.  33 

in  its  cement.  We  would  find  the  limestone  of  the  western  column  repre- 
sented only  by  more  or  less  calcareous  matej'ial  in  the  fine  sediments  of 
the  corresponding  part  of  the  eastern  column,  and  by  a  rather  abrupt 
lateral  transition  through  flaggy  limestones  and  marls,  containing  more 
quartz  sand  at  the  bottom  and  more  clay  at  the  top.  Above  this  horizon 
we  would  find  the  fine  sediments  alike  common  to  both  columns  and 
extending  far  both  to  the  east  and  the  west. 

Analyzing  the  different  horizons  we  find  along  the  west  side  of  Hoosac 
mountain  different  conditions  of  sedimentation  aff'ecting  the  horizons  of  both 
the  grit  and  the  limestone.  To  the  east  the  grit  becomes  a  conglomerate 
abounding  in  granitic  pebbles  and  in  detrital  feldspar.  To  the  east  also  the 
limestone  passes  into  shoreward  argillaceous  sediments.  Higher  up  we  find 
in  the  uniformly  widespread  fine  sediments  the  evidence  of  changed  condi- 
tions, which  through  a  long  period  excluded  to  a  great  extent  the  formation 
of  limestones  over  the  whole  region. 

Such  in  a  general  way  was  the  differentiated  character  of  the  rocks  upon 
which  the  processes  of  metamorphism  acted.  These  processes  resulted  in 
changing  the  quartz  sandstone  of  the  Cambrian  grit  into  a  quartzite,  and  the 
shoreward  feldspathic  sandstone  into  a  highly  crystalline  gneissi.  The  Cam- 
bro-Silurian  limestone,  the  limestone  proper,  was  changed  to  crystalline 
limestone;  its  shoreward  transitions  into  more  or  less  calcareous  gneiss  and 
its  more  eastward  calcareous  shales  into  a  garnetiferous  variet}^  of  the  albitic 
schist,  into  which  the  whole  column  of  Cambro-Silurian  fine  sediments  above 
the  lower  Cambrian  grit  has  been  changed.  In  the  finer  sediments,  the 
uniform  character  above  the  horizon  of  the  limestone  resulted  in  a  uniform 
change  into  a  mica-schist  characterized  by  the  general  presence  of  albite  in 
macroscopic  or  microscopic  crystals. 

We  do  not  yet  know  to  what  depth  these  rocks  were  buried.  They 
ha.ve  in  themselves  an  aggregate  thickness  of  5,000  feet  or  more.  Certainly 
if  they  were  covered  by  the  great  thickness  of  material  represented  in  the 
schists  between  Hoosac  mountain  and  the  Connecticut  river,  they  were 
buried  to  a  point  of  load  and  temperature  sufficient  to  satisfy  these  condi- 
tions of  metamorphism. 

Throughout  the  whole  region  all   the   rocks  above  the  pi-e-Cambrian 

MON  XXIII 3 


34  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

have  been  subjected  to  the  action  of  great  lateral  pressure,  throwing  them 
into  folds  and  along  certain  lines  into  compressed  and  ruptured  overfolds, 
subjecting  the  constituent  particles  to  crushing  or  shearing  and  to  move- 
ments which  are  now  marked  by  the  crinkling  of  the  original  stratification 
lamination,  and  by  the  predominant  cleavage  resulting  from  movement. 

There  were  therefore  present  the  three  factors  of  load,  temperature, 
and  attrition  of  particle  on  particle  produced  during  the  folding  movement. 
These  factors  were  essential  in  the  process  of  metamorphism,  but  they  could 
not  change  ordinary  clay  sediments  into  schists  consisting  largely  of  mag- 
nesia and  potash  micas  and  abounding  in  soda-feldspars,  nor  could  they 
change  a  grit  of  quartz  and  microcline  detritus  into  a  gneiss  consisting  largely 
of  soda-feldspar.  Either  the  original  sediments  must  have  contained  all  of 
the  elements  required  to  form  by  recrystallization  the  present  constituent 
minerals,  or  a  part  must  have  been  contributed  from  elsewhere.  The 
extreme  rarity  of  observed  eruptive  dikes  and  of  pegmatite  veins  outside 
of  limited  areas  makes  it  hard  to  explain  the  difference  between  the  chemical 
constitution  of  the  schists  in  their  great  breadth  and  thickness  and  that  of 
ordmary  argillaceous  sediments  by  ascension  from  below.  It  would  there- 
fore appear  more  likely  that  the  original  sediments  were  of  an  exceptional 
character.  They  may  have  been  deposited  under  conditions  favorable  to 
the  preservation  of  magnesium  and  alkaline  salts — conditions  which  we  know 
have  at  ^various  times  existed  over  large  areas. 

In  the  case  of  the  Lower  Cambrian  grit  the  action  of  mineralizing 
processes  originating  below  is  more  pi-obable.  Where  the  rocks  have  been 
subjected  to  the  different  forms  of  readjustment  of  particles  during  the  great 
folding  of  the  strata,  a  change  occurs  from  a  gi'it  containing  much  detrital 
microcline  to  a  highly  crystalline  gneiss  with  a  predominant  soda  feldspar, 
Avhich  bears  evidence  of  being  crystallized  in  situ.  Along  these  zones 
we  find  veins  and  "flames"  of  pegmatite,  and  in  the  crushed  quartzite  proper 
perfect  little  crystals  of  tourmaline  often  appear  in  great  abundance.  The 
very  feldspathic  veins  along  these  zones  of  extreme  folding  in  the  grit  may 
stand  related  causally  to  the  lenses  of  qiiartz  and  tourmaline,  with  and 
without  feldspar,  which  occur  rather  frequently  in  the  higher  schists  along 
the  west  flank  of  Hoosac  mountain;  also  along  the  zone  of  extreme  folding. 


\ 


F^RT    II. 


THE  GEOLOGY  OF  HOOSAC  MOUNTAIN 


ADJACENT  TERRITORY. 


J.  E.   M^OLFF. 


35 


CONTENTS 


Page. 

Introduction 41 

Topograpliic!  work 41 

Toijography 41 

Description  of  rocks  of  Hoosac  mountain 44 

The  Stamford  gneiss 45 

The  Vermont  formation : 48 

The  Hoosac  schist 59 

>         The  Stockbridge  limestone 64 

Amphibolites 65 

Geology 69 

The  Hoosac  tunnel 69 

The  region  embracing  the  central  part  of  Hoosac  mountain 72 

The  northern  and  eastern  schist  area 86 

The  region  south  of  Cheshire  and  of  tlie  Hoosic  valley 88 

Hoosic  valley  schist 97 

The  region  around  Clarksburg  mountain  and  Stamford,  Vermont 98 

General  conclusions 102 

Descriptions  of  plates 109 

37 


ILLUSTRATIONS 


XI.  ^ 


Page. 

Plate  IV.  Detailed  map  of  western  crest  and  slope,  Hoosac  mouutain 40 

V.  Geologic  proflle.s,  Hoosac  mountain 70 

VI.  Geologic  profiles,  generalized,  Hoosac  mountain 80 

VII.  Thin  sections,  white  gneiss 110 

VIII.  Thin  sections,  white  gneiss  and  albite  schist 112 

IX.  Thin  sections,  diorite  and  amphibolite 114 

X.  Thin  sections,  quartzite  conglomerate  and  crumpled  metaraorphic  conglomerate 116 

(  View  north  over  crest  of  Hoosac  mountain 118 

B  \  Profile  of  Hoosac  mountain  from  Spruce  hill  south,  looking  west 118 

Fig.    9.  View  from  Hoosac  mountain _. 43 

10.  Profile  of  Hoosac  mountain  (western  crest) 43 

11.  Profile  of  Hoosac  mountain  (western  slope) 44 

12.  Granitoid  gneiss 45 

13.  Metamorphic  conglomerate,  showing  crushing 48 

14.  Metamorphic  conglomerate,  showing  shape  of  pebbles 49 

15.  Metamorphic  conglomerate,  flattened  pebbles 50 

16.  Metamorphic  conglomerate,  round  and  flat  pebbles 51 

17.  Metamorphic  conglomerate,  banded  variety 53 

18.  Metamorphic  conglomerate,  typical 55 

19.  Metamorphic  conglomerate,  showing  large  pebbles 57 

20.  Conglomerate,  clitf 58 

21.  Albite-schist,  Hoosac  schist 59 

22.  All)ite-schist,  Hoosac  schist... 61 

23.  Albite-sohist,  Hoosac  schist 62 

24.  Mount  Holly  amphibolite 65 

25.  Mount  Holly  amphibolite 66 

26.  Mount  Holly  crumpled  amphibolite '. 67 

27.  Contact  of  granitoid  gneiss  and  metamorphic  conglomerate 73 

28.  Contact  of  granitoid  gneiss  and  quartzite,  Stamford  dike,  looking  north 100 

29.  Contact  of  granitoid  gneiss  and  quartzite,  Stamford  dike,  looking  east 101 

39 


3    GEOLOGICAL  SURVEY 


MONOGRAPH  XXin   PL  T/ 


THE  GEOLOGY  OF  HOOSAC  MOUNTAIN  AND  ADJACENT  TERRITORY. 


By  J.  E.  Wolff. 


INTRODUCTION. 

The  territory  embraced  in  this  report  extends  from  the  Hoosic  valley 
in  the  west  to  the  meridian  of  73°  on  the  east,  and  from  the  state  line  on 
the  north  to  the  valley  in  the  south  which  runs  east  from  Pittsfield  through 
Dalton.  It  covers  the  easterly  half  of  the  "  Greylock  sheet"  of  the  new  map 
of  Massachusetts.  It  is  an  area  about  18  miles  in  length,  varying  from  10 
to  4  miles  in  width,  and  covering  about  120  square  miles. 

TOPOGRAPHIC  WORK. 

As  the  extreme  complication  of  the  field  required  great  accuracy  in  the 
location  of  ovitcrops,  at  an  early  stage  in  the  work  a  base-line  7,000  feet 
long  was  meastired  on  the  Boston  and  Albany  railroad  in  Hoosic  valley  and 
a  sufficient  number  of  points  were  established  by  triangulation  to  allow  the 
accurate  vertical  and  horizontal  topographic  determination  of  important  out- 
crops, which  were  then  plotted  on  a  large  field  map  on  a  scale  of  1,000 
feet  to  the  inch.  Subsequently  the  plane-table  sheets  of  the  state  map  (scale 
2  inches  to  the  mile)  were  utilized,  and  a  special  topographic  map  of  that 
part  of  Hoosac  mountain  near  the  tunnel  (on  a  scale  of  1,000  feet  to  the 
inch)  was  prepared.  At  many  places  accurate  section  lines  were  run  by  the 
stadia  and  the  geological  points  incorporated  in  the  general  map. 

TOPOGRAPHY. 

Hoosac  mountain  is  the  name  applied  to  a  part  of  the  Green  mountains 
situated  in  the  northwest  corner  of  the  state  of  Massachusetts,  near  the  Ver- 
mont boundary.     This  region  forms  the  watershed  between  the  Hoosic  and 

41 


42 


HOOSAC  MOUNTAIISr. 


Deei-field  rivers,  branches  of  the  Hudson  and  Connecticut,  respectively.  At 
its  southern  end  it  is  di-ained  by  branches  of  the  Hoosatonic  and  by  the 
Westfield  river,  a  branch  of  the  Connecticut. 

The  entire  mountain  mass  is  cut  through  at  its  central  part  from  east  to 
west  by  the  Hoosac  tunnel,  nearly  5  miles  long,  the  tunnel  passing  almost 
directly  under  the  highest  point  of  this  part  of  the  mountain,  a  knob  one- 
half  mile  north  of  Spruce  hill,  which  is  2,600  feet  above  the  sea.  At  the 
extreme  north  of  the  field,  half  a  mile  south  of  the  Vermont  line,  the  highest 
point  is  found  to  be  2,800  feet.  Where  the  tunnel  crosses  the  central  part 
of  the  mountain  the  outline  is  that  of  a  double  crest  with  a  central  basin  or 


Fig.  9.— View  looking  west  from  alope  of  Hoosac  mountain,  east  of  North  Adams.    This  gives  a  general  idea  of  the 
topography  of  the  valley. 

depression  (see  Profile  iii,  PI.  v),  the  two  sides  joining  at  the  north  end  to 
form  the  high  north  point  and  to  terminate  the  basin. 

In  its  southern-central  portion  the  mountain  loses  the  north  to  south 
ridges  and  drainage.  It  is  tliere  characterized  by  flat,  rounded  summits 
and  gentle  depressions,  and  a  frequent  east  to  west  trend  of  the  valleys. 
A  glance  at  the  strike  and  distribution  of  the  formations  will  show  that  the 
frequent  east  to  west  strike  and  extreme  crumpling  of  the  white  gneisses 
which  occupy  this  region  cause  this  diff"erence  in  the  topography.  In 
the  southern  part  of  the  field  a  north  to  south  strike  of  considerable  regu- 


GREEN  MOUNTAmS  IN  MASSACHUSETTS. 


43 


larity  again  comes  in,  causing  a  more  ridge-like  topography,  until  the  deep 
east  to  west  valley  of  Dalton,  a  mile  or  so  south  of  the  map  (PI.  i),  bounds 
the  region  on  the  south. 

On  the  east  the  mountain  joins  the  hilly  country  extending  to  the 
Connecticut  river;  on  the  west  the  bi'oad  Hoosic  valley,  running  noilh  and 
south,  bounds  Hoosic  mountain  and  separates  it  from  the  mass  of  |Grreylock 
mountain,  the  highest  in  the  state.     (See  Fig.  9).  ( 

The  relations  of  topography  to  geological  stnicture  are  ofbfen  notice- 
able.   The  whole  eastern  border  of  the  area  shown  on  the  map  is  covered 


Fig.  10 — Profile  of  part  of  west  crest  of  Hoosac  mountain,  looking  cast  from  Hoosic  valley  opposite  Adams. 

This  shows  the  continneil  northerly  pitch  of  the  axissome  miles  sonth  of  point  sho\Yii  in  PI.  XI,  B.  The  snmmit  in  the 
right  center  is  of  white  gneiss  (Vermont  formation)  with  a  little  indistinct  minor  ridge  of  the  Hoosac  schist  trough,  both 
slanting  to  the  left  (north). 

by  the  schists,  characterized  by  a  uniform  north  to  south  strike  and  steep 
easterly  dip  of  their  structural  planes;  and  the  ridge  topography,  with  deep 
cross-goi'ges  for  the  streams,  is  evidently  due  to  that  structure. 

The  long  crest  of  Hoosac  mountain,  forming  the  main  watershed, 
coincides  in  direction  and  position  with  the  axis  of  the  northerly  pitching 
fold  which  forms  the  principal  feature  of  the  mountain,  and  with  the  axis 
of  the  central  core  of  granitoid  gneiss.     The  presence  of  the  limestone  in 


44 


GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 


the  Hoosic  and  Dalton  valleys  determined  these  depressions,  as  is  always 
the  case  with  that  rock. 

The  profile  of  Hoosac  mountain  shows  plainly  the  northerly  "  pitch"  ^ 
of  tlie  formations  by  the  gentle  slopes  to  thQ  north  and  the  bluffs  facing 
south.  (See  Fig.  10  and  PI.  xi,  b.)  The  western  slopes  of  Hoosac  mountain 
running  down  to  the  Hoosic  valley  are  steep,  but  have  a  marked  series  of 
buttresses  or  benches.     (See  Fig.  11.)     The  ckift-covered  Hoosic  valley  is 


Fig.  11. — Profile  of  west  slope  of  Hoosac  mountaiD,  from  Hoosic  valley  opposite  Adams,  looking  north. 
This  figure  shows  the  buttressed  character  of  the  west  slope  of  the  mountaiQ  at  the  left  ceuter.    These  IfuttreBSes  are 
of  crumpled  white  gneiss  (Vermont  formation),  with  a  gentle  easterly  dip. 

comparatively  flat,  sending  branches  into  the  mountain,  Avhich  are  locally 
called  "coves."     At  Cheshire  the  valley  makes  a  sharp  turn  to  the  west. 

DESCRIPTION    OF   THE   ROCKS    OF   HOOSAC   MOUNTAIN. 

The  rocks  of  this  region  are  thoroughly  crystalline,  but  little  trace 
remaining  in  general  of  their  original  elements,  whether  of  detrital  or  erup- 
tive origin,  but  the  bedding  corresponding  to  the  original  planes  of  deposit 
is  well  marked,  and,  under  the  proper  conditions,  we  can  therefore  deter- 
mine the  order  of  succession. 


'  Meaning  that  the  axes  of  the  folds  are  inclined  or  "  plunge  "  in  that  direction. 


HOOSAC  MOUNTAIN. 


45 


THE  STAMFORD  GNEISS. 

The  basement  rock  is  a  coarse  granitoid  gneiss,  which  forms  the  core 
of  Hoosac  mountain  proper,  occupying  the  surface  of  the  mountain  for 
several  miles,  .then  disappearing  below  the  overlying  rock,  but  cut  in 
Hoosac  tunnel  for  nearly  5,000  feet;  hence  this  rock  figures  prominently 
on  the  dumps  of  the  tunnel  shafts.  Another  area  of  the  same  rock  under- 
lies the  fossiliferous  Cambrian  quartzite  of  Clarksburg  mountain,  north  of 
Williamstown,  continuing  some  miles  northward  into  Vermont — the  "Stam- 
ford granite"  of  the  Vermont  geological  report. 


Fig.  12. — Granitoid  gnei8.s  (Stamford  gneiss),  from  dump  Central  shaft.    Natural  size. 

Tliis  is  the  variety  with  a  well-marlied  gneissoid  structure.    The  dark  streaks  are  composed  of  the  micas  inclosing 
irregularly  lenticular  areas  of  feldspar  and  quartz. 

In  its  most  typical  form  the  rock  is  a  coarse  banded  gneiss  (see  Fig.  12), 
composed  of  long  lenticular  crystals  of  pinkish  feldspar,  flattened  lenses  of 
blue  quartz,  and  thin,  irregular,  greenish  layers  of  a  micaceous  element 
(biotite  or  muscovite,  or  both)  mixed  with  small  epidote  crystals,  which 
cause  in  part  the  greenisli  color.  We  notice  at  once  that  tlie  broad  cleav- 
ages of  the  feldspar  often  do  not  reflect  as  one  surface,  but  as  a  num- 
ber of  little  disconnected  areas,  which  are  often  curved — a  well-known 


46  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

effect  of  great  pressure  in  crystalline  rocks.  The  feldspars  contain  little 
dull  grains  of  quartz,  black  specks  of  mica,  and  crystals  of  magnetite,  and 
are  often  crossed  by  little  branches  from  the  layers  of  mica  outside.  At 
the  edges  the  feldspars  often  pass  very  irregularly  into  the  quartz,  which 
then  forms  the  narrow  parts  of  the  lens  of  which  the  feldspai*  forms  the 
center  ("  Augen"  structure). 

The  quartz  is  characteristically  blue,  but  when  crushed  by  pressure  in 
the  rock  is  often  white  or  sugary  in  appearance,  the  blue  cores  then  rep- 
resenting the  uncrushed  material.  In  other  varieties  of  this  rock  it  has 
almost  the  structure  of  a  coarse  granite.  The  quartz  is  deep  blue,  the 
feldspar  colorless  and  in  Carlsbad  twins,  and  the  mica  layers  black.  The 
gneissic  structure  is  almost  wanting. 

Certain  other  variations  occur  in  the  structure  of  the  gneiss.  In  the  bed 
of  Roaring  brook,  Stamford,  Vermont,  the  gneiss  on  the  weathered  surface 
has  numerous  rounded  elliptical  masses  which  by  the  absence  of  quartz 
and  scarcity  of  mica  stand  out  by  contrast  with  the  rock  as  a  whole,  and 
look  like  pebbles.  They  are  composed  of  feldspar  aggregates  and  flakes 
and  patches  of  biotite.  The  microscope  shows  that  these  feldspars  are  mi- 
crocline  with  some  plagioclase  and  perhaps  orthoclase;  they  have  the  gen- 
eral structure  of  the  gneiss  itself,  without  the  quartz,  and  are  probably  of 
contemporaneous  origin.  West  of  Stamford  village  the  rock  contains  Carls- 
bad twins  of  microcline  an  inch  or  two  across,  which  weather  out  from  the 
rock,  become  rounded  by  decay,  and  look  like  pebbles. 

The  microscopic  characters  of  this  rock  are  quite  uniform;  the  large 
feldspars  are  generallv  microcline,^  with  whatever  crystalline  boundary  they 
may  have  once  possessed  obliterated  by  the  great  mechanical  changes  they 
have  undergone.  The  crystals  are  often  faulted  and  the  edges  crushed; 
little  veins  of  secondary  quartz,  mixed  with  little  grains  or  crystals  of  an 
un  striated  feldspar  (albite?)  traverse  them  along  the  fault  lines.  (See  PI. 
VII,  B.)  With  a  low  power  the  feldspar  substance  appears  cloudy,  owing  to 
fluid  cavities  ajid  little  prisms  of  epidote  in  great  numbers.  These  epidote 
grains  are  sometimes  arranged  parallel  to  the  twinning  planes  of  the  feld- 


'  In  the  "  Geology  of  Vermont,"  vol.  2,  p.  561,  there  is  an  analysis  of  the  feldspar  from  the  Stam- 
ford granite,  according  to  which  it  contains  from  64  to  66*  per  cent  silica,  10  to  11  per  cent  potash,  and 
2  to  3i  per  cent  soda. 


HOOSAC  MOUNTAIN.  47 

spar,  sometimes  not.  In  some  localities  the  feldspar  contains  little  round 
red  garnets.  Flakes  of  biotite  and  muscovite  and  octaliedra  of  magnetite 
are  common  inclusions. 

The  quartz  masses  show  cataclastic  changes  in  the  same  way;  the 
original  cores  of  the  blue  quartz,  themselves  somewhat  strained  (seen  by 
using  polarized  light),  are  surrounded  by  masses  of  broken  quartz,  the 
derivation  of  which  from  the  parent  mass  can  easily  be  traced.  The  finer 
grained  portions  of  the  rock  are  composed  of  little  fragments  of  microcline 
broken  off  from  the  larger  pieces,  and  small  simple  crystals,  often  simple 
twins,  of  a  feldspar  which  shows  but  rarely  the  multiple  twinning  of  pla- 
gioclase,  and  which  resembles  the  albite  of  the  schists.  The  layers  of  mica 
are  composed  of  muscovite,  often  with  a  greenish  color  like  talc,  but  easily 
identified  by  the  large  axial  angle,  flakes  of  dark  brown  biotite,  rarely 
altered  to  chlorite,  crystals  of  magnetite,  and  the  omnipresent  epidote  in 
prisms  or  small  grains  mixed  with  the  micas  or  inclosed  in  them.  There 
are  occasional  imperfect  crystals  of  apatite  and  prisms  of  zircon.  Some  of 
the  magnetite  grains  are  titaniferous,  as  can  be  seen  by  the  yellow  border  of 
titanite  derived  from  them.  In  many  slides  there  are  quite  large  crystals  of 
feldspar  which  have  no  multiple  twinning,  extinguish  parallel  to  the  cleav- 
age, and  are  perhaps  orthoclase. 

Slides  of  the  large  porphyritic  Carlsbad  twins  show  that  they  are  micro- 
cline, filled  with  irregular  bands  of  a  feldspar  which  extinguishes  parallel 
to  QoP  do,  and  is  filled  with  epidote  crystals.  Aggregates  of  biotite  plates 
associated  with  hornblende  crystals  are  common.  There  are  also  masses  of 
ilmenite  altered  in  part  to  titanite.  Sometimes  circles  of  hornblende  crys- 
tals and  biotite  plates,  which  inclose  a  core  of  aggregate  quartz,  by  their 
shape  and  occurrence  suggest  a  possible  replacement  of  garnets.  Grains  of 
quartz  and  crystals  of  zircon  are  common,  so  that  nearly  all  the  constitu- 
ents of  the  rock  occur  within  these  cr)rstals. 

What  may  have  been  the  origin  of  this  rock  it  is  impossible  to  say  with 
certainty;  it  is  evident  that  crushing  and  the  development  of  mica,  quartz, 
and  feldspar,  parallel  to  planes  of  break  and  sliding  has  had  a  great  deal  to 
do  With  the  development  of  the  parallel  structure.  Viewed  from  this 
standpoint  it  could  perfectly  well  have  been  an  eruptive  granite  modified 


48 


GEEEN  MOUNTAmS  IN  MASSACHUSETTS. 


by  metamorphism.  On  the  other  hand,  its  field  relations  show  its  close  asso- 
ciation with  and  frequent  transition  into  coarse  gneisses  which  seem  to  form 
part  of  a  detrital  series. 

THE   VERMONT   FOEMATION. 

A  somewhat  varied  series  of  rock  overlies  this  coarse  basement  gneiss. 
At  one  place  where  there  is  no  possibility  of  folding  (namely,  along  the 
pitching  axis  of  Hoosac  moimtain  (see  PL  v,  Profiles  ix,  x).  The  thickness 
of  this  series  has  been  measured  between  a  conformable  contact  with  the 
granitoid  gneiss  below  and  one  with  the  albite-schist  above;  it  is  between 
600  and  700  feet. 


Fig.  13. — Metamorphic  conglomerate  (Vermont  formation).    Dump,  Central  shaft.    One-fiftli  natural  size. 

This  represents  two  faces  of  one  block  at  right  angles  to  each  other,  the  line  showing  the  corner.  The  pehhles  are  of 
granulite  and  blue  quartz,  some  of  them  1^  inches  in  diameter.  The  ditferent  shape  of  tlie  cross-sections  in  the  two  planes 
is  noticeable.  By  looking  closely  it  will  he  seen  that  many  pebbles  are  cut  in  two  hy  dark  lines  (biotite),  showing  that 
their  present  shape  is  due  partly  to  crushing  and  the  formation  of  new  minerals.  This  is  seen  on  the  right  side,  but  not  on 
the  left. 

This  formation  contains  an  infinite  series  of  gradations  between  coarse 
gneisses  similar  to  the  basement  gneisses,  finer  grained  banded  gneisses, 
gneisses  composed  of  quartz  and  feldspar  with  but  a  small  amount  of  the 
micaceous  element,  metamorphic  gneiss-conglomerates,  ordinary  quartzite- 
conglomerates,  and  quartzites.  This  series  of  rocks  (represented  by  gneisses 
and  metamorphic  conglomerate)  occupies  a  position  in  the  tunnel  section 
on  either  side  of  the  central  core  of  granitoid  (Stamford)  gneiss;   while  a 


flOOSAC  MOUNTAIN. 


49 


second  nairow  belt  occurs  near  the  West  Portal,  adjoining  the  Hoosic 
valley  (Stockbridge)  limestone.  On  the  surface  it  occupies  a  large  area, 
especially  in  the  southern  part  of  the  field.  The  quartzites  occur  generally 
in  or  near  the  Hoosic  valley  adjacent  to  the  limestone,  associated  with 
conglomerates  and  passing  along  the  strike  into  the  granulitic  and  gneissic 
rocks  by  increase  in  the  amount  of  feldspar  and  mica.    . 


Fig.  14.— Metamorphic  conglomerate  (Vermont  formation).    Dump,  Central  shaft.    Two-ninths  natural  size. 
I'lie  larger  pebbles  are  mostly  granulile,  with  some  of  blue  quartz  and  feldspar.    Tliis  shows  very  plainly  the  shape  of 
the  pebbles,  which  are  but  little  elongated  in  the  plane  normal  to  the  picture. 

Beginning  with  the  simplest  rocks,  the  quartzites,  there  are  vitreous 
varieties  and  crumbly  feldspathic  varieties  passing  into  gneiss.  The 
vitreous  variety  occurs  in  large  masses  with  very  obscure  stratification, 
and  roughly  jointed.  It  varies  in  color  from  snow  white  to  yellow,  contains 
often  layers  of  mica  and  cubes  of  pyrite.     The  microscope  shows  an  even 

MON   XXIII 4: 


50 


GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 


grained,  closely  interlocking  aggregate  of  little  rounded  or  irregular  quartz 
grains  mixed  with  considerable  feldspar  in  similar  in-egular  grains.  Broken 
or  rounded  crystals  of  apatite  and  zircon  and  perfect  crystals  of  tourmaline 
and  rutile  are  common.  The  feldspar  grains  are  in  part  microcline, 
plagioclase,  and  an  untwinned  feldspar  (orthoclase  ?).  Unless  it  be  the 
apatite  and  zircon,  no  unmodified  original  clastic  elements  can  be  recognized 
in  this  rock.  According  to  the  usual  view  of  the  origin  of  quartzite,  the 
quartz  grains  have  been  enlarged  by  the  growth  of  new  silica,  so  that  the 
original  form  is  wanting,  and  the  feldspar,  judging  from  its  similarity  to 
that  of  other  i-ocks  in  which  it  is  undoubtedly  metamorphic,  has  probably  a 
similar  origin. 

In  many  localities  the  quartzites  have  a  crumbly  character,  so  that 


Fig.  15.— Metamorphic  conglomerate  (Vermont  formation),  near  contact  with  granitoid  gneiss.  Top  of  Hoosac  moun- 
tain.   Fallen  block.    One-twentieth  natural  sixe. 

This  also  pbows  the  production  of  flattened  "  pebbles  "  by  crushing  and  the  development  of  biotite,  etc.,  along  crushing 
and  slipping  planes.  In  the  right  hand  of  the  picture  this  is  especially  clear.  The  pebbles  here  are  granulite,  passing 
into  a  line  grained  granite. 

they  can  be  picked  or  shoveled  out,  and  are  extensively  quarried  for  glass 
sand.  Prof  J.  D.  Dana  has  called  attention  to  this^  and  suggested  weather- 
ing as  a  cause,  and  connected  it  with  the  alteration  and  leaching  out  of  the 
feldspar.  In  some  of  the  quarries  the  percolating  water  cames  down  filie 
kaolin,  and  forms  beds  of  pipe  clay  in  the  bottom  of  the  quarry.     But  some 

'  On  the  decay  of  quartzite,  and  the  formation   of  sand,  kaolin,  and  crystallized  quartz.    Am. 
Jour.  Sci.,  3d  ser.,  vol.  28,  1884,  p.  448. 


HOOSAC  MOUNTAIN. 


51 


of  these  crumbly  qiiartzites  show  but  little  feldspar  and  that  quite  fresh, 
while  the  quartz  grains  show  in  the  slide  abundant  signs  of  great  pressure, 
or  even  crushing.  Some  of  these  quarries  are  located  at  sharp  folds  of  the 
quartzite,  so  that  the  crumbly  nature  of  the  quartzite  may  be  in  part  due 
''  to  a  mechanical  loosening  of  the  cohesion. 

The  pure  conglomerate-quartzites  occur  often  in  the  quartzite;  for 
instance,  the  quartzite  resting  on  the  granitoid  gneiss  (Stamford  gneiss)  of 
Clarksburg  mountain,  in  which  Mr.  Walcott  has  found  fragments  of  trilo- 
bites.^  contains  pebbles  of  blue  quartz,  which  are  often  only  distinguishable 


Fig.  16.  — Metamorphic  conglomerate  (Vermont  formation).    Dump,  Central  shaft.    One-sixth  natural  aizo. 

The  pehbles  are  mostly  granulitic,  but  there  are  some  of  blue,  and  some  of  white  quartz.  In  this  type  we  have  round 
and  fiat  pebbles  ocourring  together,  the  round  ones  differing  but  little  in  shape  in  the  normal  plane.  This  represents 
the  typical  variety  of  conglomerate. 

by  their  color  from  the  surrounding  quartzite  cement.  The  microscope 
shows  that  many  of  these  pebbles  are  composed  of  an  aggregate  of  little 
quartz  grains  derived  from  a  homogeneous  mass  by  crushing,  and  hence 
they  easily  blend  with  the  quartz  cement  of  the  rock.  They  occur  often 
in  flattened  elongated  forms  which  it  is  difficult  to  distinguish  from  secre- 
tions.     (See  PI.  X,  B.) 

Some  of  the  quartzites  contain  abundant  calcite  grains  arranged  in 
stringers,  and  scattering  flakes  of  muscovite. 

Those  quartzites  in  which  feldspar  becomes  more  prominent  preserve 

'  Am.  Jour.  Sci.,  3d  ser.,  vol.  35, 1888,  p.  236. 


52  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

still  the  appearance  of  the  purely  quartzose  varieties.  The  feldspar  occurs 
in  irregular  grains  fitting  in  between  the  quartz.  It  is  partly  not  twinned 
(orthoclase?),  part  plagioclase,  generally  microline.  Little  crystals  of  rutile, 
prisms  of  zircon  and  apatite,  flakes  of  biotite  and  muscovite,  masses  of  iron 
hydrate,  pyrite,  etc.,  occur  in  nearly  all  the  specimens.  The  quartz  and 
feldspars  often  show  evidence  of  mechanical  crushing,  and  part  of  the  quartz 
has  been  thus  derived  from  larger  grains.  The  constituents  have  a  nearly 
even  grain.  Although  garnet  is  very  rare,  it  is  convenient  to  call  this  rock 
the  granulitic  type  of  the  quartzite. 

From  this  rock  tlie  transition  is  easy  to  the  white  gneiss  proper.  Sev- 
eral varieties  of  this  may  be  recognized;  a  banded  one  is  common,  the  color 
varies  from  gray,  yellow  to  white;  sometimes  the  banding  is  very  fine  or 
the  rock  is  speckled  with  biotite  or  muscovite,  or  both ;  sometimes  the  feld- 
spar forms  layers  separated  by  layers  of  mica,  or  occurs  in  rounded  or  irreg- 
ular masses.  The  proportions  of  the  elements  vary  in  every  conceivable 
way. 

A  characteristic  feature  in  the  slide  is  seen  in  the  round  grains  of  feld- 
spar of  someAvhat  larger  size  than  the  average  of  the  rock,  inclosed  in  a 
groundmass  composed  of  little  grains  of  quartz  and  feldspar  in  a  most 
intimate  admixture,  while  plates  of  mica  give  the  rock  its  banded  struc- 
ture. The  larger  sized  feldspars  are  typically  of  a  peculiar  rounded  shape, 
occurring  either  in  single  crystals  or  in  broad  simple  twins.  They  are  com- 
monly entirely  without  the  polysynthetic  twinning  of  plagioclase  in  polar- 
ized light  and  might  be  taken  for  orthoclase,  but  their  isolation  from  the 
powdered  rock  by  the  Thoulet  solution  shows  by  the  specific  gravity  that 
they  must  be  generally  a  soda-lime  feldspar  near  the  albite  end  of  the  series, 
although  in  some  rocks  they  must  cbntain  considerable  lime,  judging  by  theii* 
specific  gravity.  These  feldspars  are  commonly  filled  with  inclusions  of 
minerals  found  in  the  rock  outside  them — little  prisms  of  epidote,  flakes  of 
biotite  and  muscovite,  and  little  rounded  grains  of  quartz,  sometimes 
arranged  like  a  necklace.  These  inclusions  often  lie  in  planes  parallel  to 
the  arrangement  of  the  minerals  outside  the  feldspar,  and  entirely  inde- 
pendent of  crystallographie  directions  in  the  feldspar.  (See  PI.  vii,  a, 
and  PI.  VIII,  A.)  It  is  very  rare  to  find  any  sign  of  mechanical  deformation 
in  these  feldspars. 


HOOSAC  MOUNTAIN. 


53 


Quartz  occurs  sometimes  in  large  rounded  masses,  greatly  strained  and 
shattered,  and  surrounded  by  a  mosaic  of  small  quartz  grains.  Large  pieces 
of  microcline  occur,  faulted  and  broken,  the  cracks  filled  with  an  aggregate 
of  little  quartz  grains  and  feldspars  in  simple  twins.  (See  PI.  vii,  b.).  The 
groundmass  of  the  rock  is  a  closely  interlocking  aggregate  of  quartz  grains, 


k 


\ 


^ 


Fig.  17.— Metamorphic  conglomerate  (Vermont  formation).  Dump,  Central  shaft.  One-fifth  natural  size. 
The  tiy,nre  represents  the  banded  variety  of  the  rock,  in  which  vre  find  it  difficult  to  draw  the  line  hetween  true  pebbles 
and  forms  produced  by  crushing.  A  glance  at  the  figure,  especially  at  the  right  side,  shows  that  the  extremely  pointed  ends 
of  some  of  the  apparent  pebbles  must  he  produced  by  the  encroachment  of  the  mica  layers.  Yet  these  white  masses  have 
a  lithological  character  different  from  that  of  the  "cement,"  forming,  for  instance,  the  broad  baud  near  the  rightside.  The 
former  are  a  fine  grained  granite  or  granulite,  sometimes  blue  quartz ;  the  latter  a  coarser  grained  mixture  of  quartz,  mica, 
and  some  feldspar. 

little  feldspar  gi^ains  simply  twinned  (if  at  all)  and  often  little  grains  of 
microcline  of  the  same  form  and  size.  Epidote  is  often  present  in  large 
quantities,  foiTning  microscopic  yellow  bands  in  the  rock,  and  inclosed  in 
the  feldspars  and  micas  in  little  prisms  and  grains,  but  not  in  the  quartz. 


54  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

Titanite,  rutile,  aud  tourmaline  occur  sparsely,  as  well  as  little  broken  prisms 
of  apatite  and  zircon  prisms.  The  micas  occm*  in  homogeneous  plates ;  the 
interwoven  sericitic  structure  is  not  common.     Magnetite  occiu's  occasionally. 

Another  variety  of  these  gneisses  is  distinguished  by  the  evenness  of 
its  character  and  its  occurrence  along  the  base  of  Hoosac  mountain  as  the 
most  western  band  of  the  gneisses,  in  close  connection  with  the  quartzites 
and  limestones.  The  rocks  thrown  out  from  the  "well"  shaft,  a  few  hun- 
dred feet  west  of  the  west  shaft  of  the  tunnel,  are  typical  of  this  variety. 
In  the  hand  specimen  the  rock  is  a  fine  grained,  evenly  banded  gray  gneiss; 
the  minerals  are  arranged  in  layers  and  the  rock  is  filled  with  little 
squarish  feldspars.  In  the  slide  these  feldspars  are  seen  in  gently  rounded, 
eqiiidimensional  crystals,  in  simple  twins,  according  to  the  albite  law.  The 
groundmass  is  composed  of  little  round  or  ellipsoidal  quartz  grains  and 
more  angular  pieces  of  feldspar  (which  are  in  part  in  simple  grains,  in  part 
doubly  twinned  microcline)  mixed  with  threads  of  muscovite  and  biotite, 
the  whole  so  arranged  as  to  produce  a  schistose  structure  in  the  rock.  (See 
PI.  VII,  A,  and  PI.  VIII,  a.)  Sometimes  a  band  of  mica  and  quartz  cuts  across  a 
feldspar,  the  two  halves  polarizing  together  and  being  therefore  part  of  one 
crystal.  The  bands  of  the  groundmass  bend  around  the  porphyritic  feldspars 
in  gentle  curves.  These  feldspars  are  honeycombed  with  little  drops  of 
quartz  and  flakes  of  biotite  aud  muscovite  which  are  often  airanged  parallel  to 
the  structure  outside.  Octahedra  of  magnetite  are  visible  in  the  rock; 
microscopic  crystals  of  apatite,  rutile,  and  zircon  are  abundant.  In  some 
cases  little  grains  of  calcite  occur  abundantly,  even  included  in  the  feld- 
spars, and  in  some  localities  we  find  a  calciferous  gneiss  with  this  same 
structure,  in  which  the  groundmass  contains  a  large  amount  of  calcite  in 
little  grains  apparently  homologous  with  quartz  and  feldspar.  This  variety 
occurs  at  several  places  in  the  Hoosic  valley  near  the  junction  between 
the  limestone  and  quartzite,  and  represents  the  Hoosac  mountain  gneisses 
nearest  to  the  limestone. 

At  the  base  of  the  white  gneiss  series  the  rock  in  many  places  passes 
so  gradually  into  the  underlying  granitoid  gneiss  that  it  is  impossible  to 
draw  a  line  between  the  two.  These  varieties  of  the  white  gneiss  are 
very  coarse  and  feldspathic,  but  the  feldspars  are  white  instead  of  red  as  in 


HOOSAC  MOUNTAIN. 


55 


the  granitoid  gneiss,  and  the  mica  is  black.  In  the  shdes  the  structure  is 
essentially  the  same  as  that  of  the  granitoid  gneiss:  the  large  crystals  are 
microcline,  broken,  faulted,  filled  with  fluid  inclusions,  epidote  grains, 
quartz,  mica,  etc.;  while  the  groundmass  is  composed  of  the  usual  simply 
twinned  feldspars  and  quartz,  mixed  with  epidote,  muscovite,  biotite,  and 
other  minerals. 

At  the  upper  contact  of  the  white  gneiss  series  there  are  frequent  tran- 
sitions into  the  overlying  albite-schists  (Hoosac  schist);  the  transition  is 
caused  by  the  appearance  of  bands  of  mica  in  the  white  gneiss  alternating 
with  bands  of  feldspar.  The  latter  are  often  lenticular  and  composed  of  the 
simply  twinned  feldspars  which  in  the  schist  are  proved  to  be  albite. 


Fig.  18.— Metamorphic  coDglomorate  (Vermont  formation).    From  dump  of  Central  shaft.     About  one.fourth  natural  size. 
This  is  also  tlie  typical  conglomerate.    The  pebhles  are  mostly  of  the  fine  grained  granuUte  type.     The  tine  grained 
layers,  of  which  a  good  example  is  seen  near  the  top,  are  composed  of  quartz  grains,  hiotite,  and  some  feldspar.    They 
represent,  of  course,  sand  layers  in  the  original  sediment  which  have  undergone  considerable  metamorphism. 

The  last  and  perhaps  the  most  important  member  of  the  white  gneiss 
series  is  the  metamorphic  conglomerate.  This  rock  occupies  a  large  area 
in  the  tunnel,  occurring  on  both  sides  of  the  central  core  of  granitoid  gneiss. 
Nearly  all  the  varieties  of  the  rock  are  well  shown  by  the  dumps  of  the 
central  and  west  shafts  of  the  tunnel.  On  the  surface  it  is  found  on  the 
crest  of  the  mountain  in  the  line  of  the  axis  of  the  fold,  where  the  rocks 
have  a  gentle  northerly  dip,  and  measured  between  conformable  contacts 
with  granitoid  gneiss  below  and  schist  above,  it  has  a  thickness  of  about 
650  feet. 


56  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

The  rock  contains  pebbles  of  two  varieties :  one  kind  composed  of  bright 
blue  opalescent  quartz,  the  other  resembling  a  fine  grained  granite,  composed 
of  quartz  and  feldspar  in  small  grains,  speckled  with  biotite.  These  pebbles 
on  tlie  average  are  as  large  as  a  walnut,  though  some  are  much  larger, 
and  they  diminish  in  size  until  undistinguishable  from  the  elements  of  the 
groundmass.  The  shape  is  sometimes  round,  sometimes  ellipsoidal,  angular, 
or  flattened.  In  Fig.  13,  which  gives  two  sides  of  a  large  block,  the  different 
cross-section  of  the  pebbles  in  two  planes  is  shown.  The  groundmass  or 
cement  outside  is  composed  of  smaller  grains  of  blue  quartz,  small  feldspars 
resembling  the  albite  of  the  schist,  and  biotite  and  muscovite  in  large  amount. 
The  effects  of  crushing  in  the  rock  are  evident;  the  pebbles  are  often  trav- 
ersed by  parallel  breaks  or  oblique  cracks  by  which  bands  of  biotite  pene- 
trate them,  isolating  parts  of  the  pebble.  Sometimes  a  pebble  is  cut  in  two 
across  its  axis  by  such  a  band  of  mica.  Thus  pebbles,  in  appearance  sepa- 
rate, may  have  been  parts  of  one  individual  originally.  This  crushing  action, 
combined  with  the  formation  of  the  biotite  bands,  gives  many  of  these  origi- 
nal pebbles  flattened  shapes,  so  that  they  appear  as  layers  of  granitic  mate- 
rial cut  off  by  the  biotite  bands  in  planes  oblique  to  their  trend.  Some 
varieties  of  this  conglomerate  gneiss  have  a  banded  structure,  due  in  large 
part  to  this  crushing  actioii  carried  to  an  extreme.  (See  Fig.  17.)  In  some 
cases  the  pebbles  are  single  crystals  of  feldspar,  and  this  is  occasionally 
microcline. 

Figs.  13-20  show  the  character  of  this  rock.  Some  of  the  pebbles 
consist  of  fine  grained  granite  containing  small  grains  of  blue  quartz.  Fine 
grained  gneissoid  layers  corresponding  to  the  cement  often  alternate  with 
pebbly  layers  (see  Fig.  18).  In  some  varieties  these  granite  pebbles  lie  in 
a  very  micaceous  matrix,  composed  of  small  feldspars  resembling  those  of 
the  schist;  in  others  the  pebbles  become  so  small  that  we  get  an  even  banded 
gnejss  containing  larger  grains  of  blue  quartz,  the  whole  forming  the  ordi- 
nary Avhite  gneiss  previously  described.  It  is  then  very  difficult  or  impossible 
to  separate  the  old  quartz  and  feldspar  from  that  formed  in  situ.  The  opal- 
escent blue  quartz  pebbles  always  retain  their  round  form  and  are  rarely 
entered  by  the  biotite  outside.  This  shows  perhaps  a  connection  between  the 
formation  of  the  biotite  and  the  feldspar  substance.  The  previous  description 
is  based  on  the  conglomerate  of  the  tunnel  dumps. 


HOOSAO  MOUNTAIN.  57 

On  the  surface  here  and  there  conglomerates  are  found,  often  associ- 
ated with  quartzites;  in  the  latter  case  the  pebbles  are  all  quartz  and  the 
cement  is  composed  of  biotite,  muscovite,  small  feldspar,  and  magnetite 
crystals. 

On  the  crest  o(  Hoosac  mountain,  in  Profile  ix,  PI.  v,  the  conglomerate 
is  represented  principally  by  the  finer  grained  varieties,  but  toward  the  base 
the  pebbles  are  much  larger  and  are  in  part  not  pebbles,  but  fragments  of 
layers  broken  up  by  crushing  (see  Figs.  15  and  27),  giving  angular  forms. 

When  we  pass  westward  from  the  crest  of  Hoosac  mountain,  where 
the  conglomerate  lies  in  its  normal  position,  we  trace  the  rock  into  the 
white  gneiss  series  on  the  slopes  of  the  mountain.     The  pebbles  have  lost 


Fio.  19.— Metamorphic  conglomerate  (Yermont  formation) .    Dump,  Central  shaft.    About  one-seventh  natural  size. 

In  this  variety  the  pebbles  are  of  much  larger  size  (over  5  inches  long),  they  have  the  most  perfect  beach-pebble  shape, 
and  are  composed  of  a  very  fine  grained  granite,  which  contrasts  sharply  with  tlie  much  coarser  gneissoid  cement  composed 
of  quartz  and  feldspar  grains  and  mica  fl.il£es.    The  long,  white,  irregular  masses  in  the  center  are  secondary  vein  quartz 

their  distinctness,  and  without  the  favorable  exposui-es  on  the  summit  and 
from  the  tunnel  we  would  not  suspect  their  nature;  they  appear  as  white, 
flat,  lenticular  masses  of  quartz  and  feldspar,  which  only  in  rare  places  sug- 
gest a  conglomerate  (see  PI.  x,  b),  but  when  one  has  traced  this  rock  foot 
by  foot  into  the  conglomerate  he  recognizes  the  pebbly  look  at  once.  It  is 
apparent  that  this  change  is  connected  with  stretching  of  the  rock,  for  the 
conglomerate  is  folded  over  and  then  turned  under  on  the  west  flank  of  the 
mountain. 

The  microscope  shows  that  the  quartz  pebbles  are  homogeneous  masses 


58 


GEEEN  MOUNTAINS  IN  MASSACHITSETTS. 


of  quai"tz,  wliicli  by  optical  investig-ation  are  seen  to  lia^-e  been  greatly 
strained;  they  have  a  border  of  l)roken  quartz  which  grades  into  the  ground- 
mass.  (See  PI.  X,  A.)  They  are  identical  with  the  blue  quartz  pebbles 
ofthefossiliferous  Cambrian  conglomerate  (Vermont  formation)  farther  west 
(Clarksburg  mountain,  Stone  hill).  The  granite  pebbles  are  composed  of 
crystalloids  of  microcline,  plates  of  biotite,  and  grains  of  quartz.  The  micro- 
cline  and  quartz  are  crushed  and  faulted.  Veins  of  a  later  quartz  traverse  the 
fissures  in  the  feldspars.     Crystals  of  zircon  and  apatite  and  plates  of  chlo- 


FiG.  20.— Conglomerate  (Vermont  formation).    Crest  of  lloosat  luuuutiiiu  south  of  Sprace  hill. 

This  sbows  a  large  clifl'  of  the  conglomerate  as  it  occurs  in  place.    The  pebbles  here  are  largely  blue  and  white  quartz 
and  the  cement  gneissoid.    This  is  in  the  upper  half  of  the  conglomerate  horizon. 

rite  occur  in  the  feldspar.  There  are  skeleton  crystals  of  magnetite  asso- 
ciated with  the  apatite.  The  cement  is  quite  similar  to  that  of  the  white 
gneiss. 

Without  here  going  into  the  much  disputed  question  of  metamorphic 
conglomerates  in  general,  which  are  found  in  so  many  terranes  of  stratified 
crystalline  rocks,  ^  it  may  be  said  that  the  reasons  for  considering  this  par- 
ticular rock  a  true  conglomerate  and  not  a  gneiss  containing  peculiar  con- 

'  Cf.  A.  Winchell,  Am.  Geologist,  vol.  3,  pp.  143  and  256.    Also  C.  H.  Hitchcock,  Am.  Geologist, 
vol.  3,  p.  253. 


HOOSAO  MOUNTAIN. 


59 


cretionaiy  forms,  are,  first,  the  shape  and  distribution  of  these  forms  (well 
shown  in  the  fignres)  and  the  alternations  parallel  to  the  stratification  (deter- 
mined by  contact  with  other  rocks)  of  bands  of  coarse  and  fine  material; 
second,  the  diverse  nature  of  the  pebbles  in  the  same  rock  (blue  quartz, 
white  quartz,  granulitic  rock,  granite,  etc.) ;  and,  third,  the  frequent  transi- 
tions in  the  field  into  quartzite  and  quartzite-conglomerate.  The  production 
of  at  least  part  of  the  mica,  feldspar,  and  quartz  of  the  cement  in  situ  has  been 
indicated,  and  also  the  efi'ects  produced  by  crushing. 


THE   HOOSAC   SCHIST. 


The  next  member  of  the  series  is  the  albite-schist  (see  Figs.  21,  22,  23, 
and  PI.  VIII,  b),  Avhich  confoiTnably  overlies  the  conglomerate  on  top  of 


Fig.  21.— Albite  schist  (Hoosac  schist).    Dump,  Central  shaft.     Ouetwclfth  natural  size. 
This  is  the  type  with  thin  Hat  quartz  layers  (the  white  streaks)  and  gentle  crumpling. 

Hoosac  mountain,  extending  northward  for  miles  into  Vermont.  On  the  east 
it  extends  southward  along  the  east  side  of  the  conglomerate  and  on  the  west 
in  a  narrow  band  along  the  west  slopes  of  the  mountain,  curving  around  so 
as  to  almost  join  that  on  the  east.  In  Hoosic  valley  masses  of  these  schists 
occur  adjoining  the  Stockbridge  limestone  and  then  lying  between  it  and 
the  Hoosac  gneisses  of  the  Vermont  formation.  In  the  tunnel  a  band  occurs 
several  thousand  feet  wide  (see  PI.  v,  Profile  in)  between  the  west  band 


60  GEEEJSr  MOUNTAINS  IN  MASSACHUSETTS. 

of  white  gneisses  and  those  of  the  eastern  core,  and  again  at  about  tne  cen- 
ter of  the  tunnel,  under  the  central  shaft,  they  come  in  east  of  the  con- 
glomerate and  fill  the  eastern  half  of  the  tunnel  to  about  6,000  feet  from 
the  east  portal,  where  they  are  succeeded  by  the  silvery -green  schists  (Rowe 
schists)  to  the  east  portal. 

Among  the  perfectly  fresh  material  found  at  the  tunnel  dumps  a  shiny 
black  glistening  rock  is  typical,  containing  parallel  layers  of  white  quartz 
which  thin  out  and  disappear  in  the  rock.  These  flat  lenses  are  sometimes 
very  irregular  and  crumpled  by  large  folds  or  small  puckerings.  It  is  found 
that  they  correspond  to  the  plane  of  stratification  of  the  rock  wherever  the 
schist  is  seen  in  contact  with  other  rocks.  The  black,  shiny  part  of  the 
rock  is  filled  with  sparkling  glassy  crystals  of  feldspar,  either  in  imperfect 
rounded  crystals  or  in  simple  twins,  which  contain  inclusions  of  mica,  gar- 
net, etc.  The  basal  cleavage  planes  are  sometimes  bounded  by  the  brachy- 
pinacoid  (M),  the  prisms  T  and  1,  and  the  macrodome,  etc.,  but  the  crystals 
are  in  general  rounded  or  even  angular. 

The  feldspar  twins  are  according  to  the  albite  law,  and  the  crystal  is 
di^'ided  into  two  symmetrical  halves,  or  else  the  composition-plane  is  irreg- 
ular, one  half  taking  up  most  of  the  crystal,  leaving  a  small  strip  to  the 
other.  The  rock  was  powdered  and  the  feldspar,  separated  by  the  Thoulet 
solution,  analyzed  by  Mr.  R.  B.  Riggs  in  the  laboratory  of  the  U.  S.  Greolog- 
ical  Survey  at  Washington  with  the  following  result: 

SiOi 69-69 

AljO-j 18-60 

CaO trace 

MgO 0-20 

NaiO 1028 

K.O : 0-40 

Ignition 0-42 

99-59 
COj  (Combustion),  0-77^0-44C. 

Basal  cleavage  pieces  with  the  simple  twin  give  an  extinction  4° 
oblique  to  the  twinning-plane  and  second  cleavage  (M).  Twins  measured 
in  the  goniometer  give  angles  of  172°  46'  to  172°  50'  between  the  basal 
cleavages  of  the  two  twins.  The  chemical  and  physical  properties  are 
therefore  those  of  albite.     These  albite  cr3"stals  vary  from  large  to  small; 


HOOSAC  MOCTNTAIN. 


61 


they  He  in  planes  roughly  jjarallel  to  the  schistosity  of  the  rock,  but  their 
crystallographie  directions  have  no  such  relation. 

Some  varieties  of  the  rock  at  the  shaft  are  filled  with  red  garnets  iu 
dodecahedral  crystals. 

The  surface  rock  has  the  same  characters,  but  with  certain  variations 
due  in  part  to  weathering.  The  shiny  black  variety  is  found  here  and  there, 
but  the  rock  is  commonly  greenish,  indicating  a  certain  amount  of  chlorite; 
it  varies  from  light  to  dark  green.  Garnets  are  sometimes  contained  in  the 
rock,  especially  at  the  base,  where  a  gametiferous  horizon  occurs.    Feldspar 


Fia.  22. — Albite  schist  (Hoosac  srhisti.     Dump,  Central  shaft.    One-sixth  natural  size. 

Here  the  quartz  lenses  are  more  ii-regular  and  thicker;  tlio  little  white  specks  dotting  the  rock  are  the  crystals 
of  albite. 

is  often  present  with  the  garnet.     These  schists  are  identical  in  every  detail 
with  the  schists  of  Mount  Greyiock. 

The  por])hyritic  albites  are  prominent  in  the  slide.  Simple  twins  are 
common,  but  polysynthetic  twins  rare.  Single  crystals  are  common.  They 
have  a  rounded  lenticular  or  flat  shape.  The  groundmass  outside  the  feld- 
spar is  composed  of  rauscovite  and  biotite,  or  muscovite  alone,  chlorite, 
grains  and  aggregate  lenses  of  quartz,  magnetite  in  octahedra  or  grains, 
apatite,  tourmaline,  and  rutile.     Ottrelite  is  found  in  some  localities     The 


62 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


micas  of  the  groundmass  bend  around  the  albites  in  gentle  curves  (see  PI.  viii, 
b),  and  often  a  band  of  mica  cuts  across  a  feldspar.  The  albite  contains 
inclusions  of  muscovite,  biotite,  chlorite,  quartz,  magnetite,  rutile,  etc., 
according  to  their  presence  or  absence  in  the  I'ock.  It  is  common  to  see 
them  in  curving  bands  parallel  to  the  banding  of  the  same  minerals  outside 
the  feldspar.  These  feldspars  evidently  crystallized  contemporaneously 
with  the  other  minerals  in  the  rock. 


Fig.  23. — Alliite-srbist  (Hoosac  schi.sl).    Dump,  Central  shaft.    About  one-oighth  natural  size. 

Here  the  quartz  lenses  are  agaiu  prominent.     It  i.s  found  that  they  are  always  parallel  to  the  stratitication. 


The  quartz  occurs  in  little  grains  often  arranged  in  stringers.  The  mus- 
covite is  either  in  stout  plates  or  is  a  mass  of  interlacing  fibers  or  plates — 
the  structure  characteristic  of  sericite.,,  Biotite  and  chlorite  occur  in  plates 
or  irregular  scales;  the  two  minerals  occur  sometimes  side  by  side  in  the 
same  piece  without  any  sharp  boundary  between   the  two,  so  that  the 


HOOSAO  MOUNTAIN.  63 

chlorite  has  the  appearance  of  an  alteration  product  of  the  biotite.^  When 
the  chlorite  occurs  inde})eudently  in  stout  plates  it  has  a  marked  pleoclu-oism 
varying  fronl  green  to  yellow  green,  an  extinction  several  degrees  oblique 
to  the  cleavage  and  twinning  with  OP  as  composition-plane.  Tourmaline 
and  apatite  occur  in  imperfect  prisms,  magnetite  in  octahedi'a,  and  rutile  in 
small  crystals,  often  with  the  heart-shaped  twins. 

In  several  specimens  a  little  ottrelite  has  been  noticed,  and  at  one  local- 
ity this  mineral  occurs  in  such  amount  that  tlie  rock  must  be  called  an 
ottrelite-schist.  This  is  interesting  in  that  it  still  further  proves  the  litho- 
logical  identity  of  the  Hoosac,  Greylock,  and  Berkshire  schists,  since  this 
mineral  is  found  in  all  three  of  these  formations.  The  hand  specimen  is  a 
shiny,  gi-eeuish  schist  containing  crystals  of  garnet  and  dotted  with  little 
black  ottrelite 'crystals.  In  the  slide  the  ottrelite  occurs  in  comparatively 
large  crystals  with  the  characteristic  indigo-blue,  vellow,  tdive-green  ple- 
ochroism.  The  extinction  is  several  degrees  oblique  to  the  cleavage;  it  is 
twinned  }iarallel  to  the  base,  and  basal  sections  give  a  faint  bisectrix.  It 
occurs  associated  with  irregular  masses  of  black  ore;  a  number  of  small 
prisms  of  ottrelite  surround  a  plate  of  the  ore  (ilmenite?).  Plates  of  mus- 
covite  and  a  few  grains  of  quartz  compose  the  rest  of  the  rock.  The 
ottrelite  is  filled  with  little  prisms  of  rutile  with  the  "knee "-twin.  Basal  sec- 
tions show  the  blue  color,  with  vibrations  parallel  to  h  (at  right  angles  to 
the  axial  plane),  and  the  yeUow  green  parallel  to  a;  hence  it  has  the  ^jle- 
ochroism  of  most  ottrelites.^ 

In  this  schist  we  recognize  no  clastic  element  with  certainty  and  the 
feldspar,  quartz,  micas,  etc.,  apjiear  to  have  formed  contemporaneously,  for 
the  feldspars  c(jiitaiu  inclusions  of  the  other  elements  and  in  turn  are  some- 
times crossed  bv  tongues  of  mica  and  qixartz. 

While  the  term  "schist"  is  applied  to  this  rock  owing  to  its  frequent 
coarsely  crystalline  character,  yet  its  great  similarity  should  be  noted  to 
crystalline  rocks  described  from  Germany  and  elsewhere  as  albite-jihi/Uites, 
which  contain  porphyritic  albites  with  similar  inclusions,  micas,  magnetite, 
etc. 

'  This  association  of  biotite  and  chlorite  is  common  in  the  hydromica  schists  of  the  Green  moun- 
tains and  is  often  suggestive  of  hydration  by  weathering. 
'^  Cf.  Rosenbusch:  Physiographie,  vol.  1,  p.  494. 


64  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


THE   STOCKBRIDGB   LIMESTONE. 


The  next  rock  is  the  hmestone  found  in  Hoosic  valley  at  the  base  of 
Hoosac  mountain  and  covering  the  valley  west  to  the  base  of  tlie  Greylock 
mountain  mass.  It  occurs  in  contact  with  the  Vermont  quartzite  and  with 
both  the  Berkshire  and  Hoosac  schists  at  several  places  in  the  valley. 

The  rock  is  generally  a  coarsely  crystalline  white  marble  banded  with 
layers  of  yellow  muscovite  or  dark  graphitic  substances,  and  containing 
layers  of  bluish  quartz.  Layers  of  quartzite  are  frequent  in  the  limestone 
and  the  change  fi-om  one  to  the  other  is  gradual.  Microscopically  the  lime- 
stone consists  of  grains  of  calcite,  a  few  of  quartz,  flakes  of  mica,  etc. 

It  has  been  mentioned  that  one  variety  of  the  fine  grained  white  gneiss 
often  contains  considerable  calcite,  thus  forming  in  some  sense  a  transition 
between  the  Stockbridge  limestone  and  the  Vermont  gneiss.  A  much  more 
perfect  transition  is  found  between  the  limestone  and  Hoosac  schist.  The 
best  case  of  this  kind  is  found  in  the  "Cove,"  in  Cheshire,  where  the  ground 
is  filled  with  large  angular  blocks  of  this  rock,  which  occurs  in  place  in  one 
ledge.  These  rocks  resemble  a  micaceous  white  limestone  filled  with  little 
dark  grains  or  imperfect  crystals  of  feldspar.  In  the  slide  the  rock  is  com- 
posed of  a  mass  of  calcite  grains,  with  here  and  there  single  grains  of 
quartz,  or  an  aggregate  of  several  grains,  plates  of  muscovite  and  often  of 
chlorite  and  biotite,  and  large  porphyritic  feldspar  grains  in  single  crystals 
or  simple  twins,  very  rarely  showing  polysynthetic  twinning.  These  feld- 
spars contain  inclusions  of  mica,  quartz,  iron  ore,  rutile,  and  calcite,  and 
are  in  every  way  identical  with  the  albites  of  the  albite-schists,  although 
the  exact  species  of  plagioclase  has  not  been  determined.  The  calcite  seems 
to  play  the  jiart  which  the  quartz  does  in  the  schists:  it  sends  tongues  into 
the  feldspars,  or  cuts  them  in  two,  and  gives  one  the  impression  by  its  in- 
clusions in  the  feldspar  and  its  occurrence  with  the  quartz  and  mica  that  it 
is  of  contemporaneous  origin  with  the  feldspar,  mica,  and  quartz.  Rutile 
needles,  and  masses  of  ore  (ilmenitef)  occur  in  curved  bands  in  these  feld- 
spars. Small  irregular  masses  of  microcline  occur  sometimes  among  the 
quartz  grains  of  the  rock. 

On  the  Greylock  side  of  the  valley  about  300  yards  west  of  Maple 
Grove  station  there  occur  outcrops  of  a  similar  feldspathic  limestone.     Part 


HOOSAC  MOUNTAIN 


65 


of  the  feldspar  is  here  in  broad  simple  twins,  but  part  is  microcline  in  simi- 
lar crystals.     The  feldspar  of  this  rock  needs  further  investigation. 

The  hne-g-rained  silvery  green  or  green  schists  (Rowe  schists)  which 
occu})y  a  strip  on  the  extreme  eastern  border  of  the  map,  overlying  the  albite- 
schist  (Hoosac),  have  not  been  microscopically  investigated  by  the  writer. 

AMPHIBOLITES. 

Last  to  be  described  are  heavy  dark  rocks,  generally  fine  grained,  in 
which  the  eye  recognizes  dark  crystalloids  of  hornblende  and  irregular 


Fig.  24.— Amiiliiliolitc.    Mount  Holly,  Vermont. 

A  band  of  aiii[iliib()Iitc  li  feet  wide,   interstratitied  with  j^neiss  and  crumpled  with  it  iu  a  laj-ge  double  fold.    The 
atructure  of  the  aujphibolite  coincides  in  every  detail  with  that  of  the  gueisa. 

patches  of  feldspar  and  cubes  of  pyrite.  In  the  finer  grained  varieties  the 
rock  has  a  glistening  surface  due  to  plates  of  biotite  in  films  mixed  with  the 
hornblende,  and  the  rock  then  has  a  somewhat  schistose  structure.  They 
rocks  have  been  found  in  several  localities,  in  all  but  one  case  in  beds  par- 
allel to  the  structure  of  the  inclosing  gneisses  and  contorted  with  them. 

These  rocks  occur  abundantly  in  the  Green   mountains.     The   most 

remarkable  occurrence  is  perhaps  near  Mount  Holly  and  Wallingford,  Vt., 
MON  xxiii 5 


66 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


70  miles  north  of  Hoosac  mountain.  Here,  too,  the  Cambro-Sikirian 
limestone  and  Cambrian  quartzite  (Vermont  formation)  are  succeeded  by 
gneissic  rocks  in  the  east,  which  form  the  central  divide  of  the  Grreen  moun- 
tains. In  the  region  east  of  Rutland  and  directly  south  of  the  high  mountain 
mass  of  the  Killington  peaks  there  is  a  marked  l)reak  in  the  general  topog- 
raphy in  an  east  to  west  zone,  10  to  15  miles  wide  from  north  to  south,  which 
is  characterized  by  the  flat  character  of  the  hills.  The  north  to  south  ridge 
character  of  the  Green  mountains  is  interrupted  here,  and  replaced  by  gently 


Fig.  25 Amphibolite.    Same  locality  as  24. 

The  amphibolite  is  Interatratified  here  with  quartzite. 

rounded  elliptical  hills  forming  an  open  grazing  country.  The  railroad  from 
Bellows  Falls  to  Rutland  crosses  the  axis  of  the  mountains  at  this  place. 
We  notice  that  the  soil  is  colored  a  deep  red  and  soon  find  that  this  is  due  to 
the  decay  of  masses  of  these  amphibolites,  which  are  interbanded  with  the 
highly  contorted  gneisses  of  the  region.  Figs.  24,  25,  26  show  this  very 
well.  These  bands  of  rock  are  parallel  to  the  strata  of  the  gneiss  in  most 
cases,  but  here  and  there  send  out  across  the  strata  tongues  which  have 
a  fine  grain  at  contact  and  show  that  these  rocks  are  intrusions.  They  have 
in  general  a  perfectly  parallel  sti-ucture,  which  curves  with  that  of  the  inclos 


HOOSAO  MOUNTAIN. 


67 


iiig  gneisses,  but  also  a  marked  columnar  jointing.  The  form  of  the  hills 
and  the  very  existence  of  this  topographical  belt  seem  due  to  the  rapid 
erosion  of  these  rocks.  Their  field  relations  show  that  they  are  of  intrusive 
origin — dikes,  in  fact,  injected  parallel  to  the  strata  and  then  crumpled  and 
metamorphosed — and  their  microscopical  characters  agree  with  those  of 
similar  rocks,  described  by  Lossen,  Teale,  and  many  others,  which  have  been 
recognized  as  altered  dikes.  They  correspond  in  part  to  the  "metamorphic 
diorites"  of  Hawes.^  They  are  briefly  described  by  President  Hitchcock 
in  the  Geology  of  Vermont,  Vol.  ii,  p.  578,  where  the  remark  is  make  that 
they  "may  be  only  huge  dikes." 


Fig.  26. — Cruniplert  ampliibolite,  Mount  Holly,  Vurmout.     Natural  size. 

The  white  bands  are  feldspar,  tlie  dark  bands  hornblende  principally.  The  vertical  groovings  which  coincide  with 
the  lino  of  apices  of  the  folds  (the  specimen  standing  as  in  nature)  show  but  faintly  in  the  figure,  and  are  doubtless  caused 
by  rain  tlowing  over  the  vertical  surface  and  following  the  depressions  between  the  small  folds. 

In  the  hand  specimen  we  see  a  dark  heavy  rock,  with  very  faint  parallel 
structure  in  the  coarse  vai'ieties.  Studied  in  thin  section  these  rocks 
have  very  uniform  characters;  the  least  altered  forms,  of  coarser  grain, 
are  composed  of  crystalloids  of  hornblende  and  rounded  grains  of  plagio- 
clase  feldspar.  The  hornblende  is  a  massive  brownish-green  variety  in 
short  irregular  crystalloids,  the  central  parts  of  which  are  filled  with  a  dark 
opaque  substance,  which,  with  high  powers,  is  resolved  into  a  mass  of  little 
crystals  of  rutile;    they  sometimes  inclose  crystals  of   apatite.     In  some 

'  Litliology  of  New  Hampshire,  p.  225, 


68  GREEN  MOUNTAINS  OF  MASSACHUSETTS. 

parts  of  the  rock  these  grains  of  hornblende  fit  in  between  rounded  grains 
of  a  twinned  plagioclase.  In  other  places  in  the  rock  the  hornblende  is 
seen  to  have  a  narrow  fringe  of  light  green  pleochroic  hornblende  (see 
PI.  IX,  b),  massive  and  not  fibrous  ;  in  other  grains  this  entirely  replaces  the 
brown  hornblende,  or  only  little  cores  of  the  latter  are  left.  At  the  same 
time  the  feldspars  in  those  parts  of  the  rock  are  filled  with  small  acicular 
crystals  of  the  same  green  hornblende  associated  with  small  grains  of  pla- 
gioclase, and  minute  veins  composed  of  these  two  minerals  often  cross  the 
original  feldspars  by  narrow  fissures  (see  PI.  ix,  a).  The  extreme  change 
consists  in  the  entire  replacement  in  parts  of  the  rock  of  the  feldspar  and 
hornblende  by  an  agg-regate  of  these  small  secondary  feldspars,  with  a 
little  quartz  and  epidote  in  abundance.  It  is  plain  that  the  original  plagio- 
clase and  brown  hornblende  has  changed  to  a  new  plagioclase,  green  horn- 
blende, some  quartz,  epidote  (taking  part  of  the  lime  from  the  feldspar),  and 
a  little  calcite. 

In  another  form  the  rock  is  a  fine-grained  amphibolite  composed  of 
crystalloids  of  bright  green  or  bluish  green  hornblende,  rarely  inclosing 
small  cores  of  original  brown  hornblende,  and  plates  of  biotite;  both  these 
minerals  lie  in  planes,  causing  the  schistose  structure.  The  remaining 
space  is  filled  with  little  plagioclases  which  are  rarely  polysynthetically 
twinned  and  are  filled  with  grains  and  prisms  of  epidote.  Grains  of 
titanite  surround  small  black  cores  of  original  titaniferous  iron  ore  and 
sometimes  the  titanite  grains  run  out  in  stringers  parallel  to  the  schistosity. 
These  feldspars  contain,  in  addition  to  e^jidote,  titanite  grains,  needles  of 
hornblende,  biotite  flakes,  and  grains  of  quartz.  In  some  rocks  the  little 
prisms  have  the  characters  of  zoisite  instead  of  epidote.  These  feldspars 
may  occur  in  broad  simple  twins  like  the  albite  of  the  schists,  or  may  be 
polysynthetically  twinned.  The  feldspar  was  isolated  from  several  rocks  by 
the  Thoulet  solution  and  found  to  be  always  plagioclase,  generally  toward 
the  albite  end  of  the  series.  The  hornblende  contains  titanite  and  epidote; 
the  plates  of  biotite  contain  rutile  needles. 

A  few  of  these  rocks  carry  irregular  masses  of  red  garnet  which  alter 
to  chlorite;  they  inclose  masses  of  magnetite  and  green  hornblende  with 
cores  of  brown  hornblende.  The  garnet  seems  to  be  contemporaneous  with 
the  feldspar. 


HOOSAC  MOUNTAIN.  69 

One  vertical  dike  of  this  rock  at  Stamford,  Vermont,  contains  blue 
quartz  grains  and  broken  crystals  of  microcline,  which  have  been  taken  from 
the  country  rock  of  the  dike,  the  granitoid  gneiss  (Stamford  granite). 

GEOLOGY. 

For  convenience  of  description  the  region  covered  by  the  map  (PL  i) 
may  be  divided  as  follows: 

First.  The  Hoosac  tunnel. 

Second.  The  region  embracing  the  central  part  of  Hoosac  mountain 
from  the  tunnel  line  on  the  north  to  the  point  in  Cheshire  where  the  crest 
of  the  mountain  makes  an  offset  to  the  west. 

Third.  The  area  covered  by  the  schists  occupying  the  northern  and 
eartern  parts  of  the  map. 

Fouilih.  The  region  south  of  Cheshire  and  of  the  Hoosic  valley. 

Fifth.  Hoosic  valley  schist. 

Sixth.  The  region  around  Clarksburg  mountain  and  Stamford,  Vermont. 

THE    HOOSAC    TUNNEL. 

This  great  engineering  work  is  4f  miles  long,  entering  the  base  of 
Hoosac  mountain  from  the  Hoosic  valley  on  the  west,  and  running  in  a 
nearly  due  east  direction  across  the  trend  of  the  range.  Two  shafts  have 
been  sunk;  the  deepest,  the  central  shaft,  near  the  center  of  the  tumiel,  is 
about  1,000  feet  deep,  descending  from  the  basin-like  depression  on  top  of 
the  mountain.  (See  PL  v,  Profile  iti).  The  other,  the  west  shaft,  is  not 
quite  half  a  mile  from  the  west  portal,  and  is  325  feet  deep.  About  1,000 
feet  west  of  the  west  shaft,  a  small  shaft  called  the  "well"  was  sunk,  on  the 
dump  of  which  specimens  of  the  rock  are  found. 

The  tunnel  itself  is  a  large  double-track  opening,  which,  starting  from 
the  Stockbridge  limestone  at  the  west  portal,  passes  through  all  the  rocks 
of  the  series  at  least  once.  But  several  tilings  combine  to  greatly  lessen  its 
value  as  a  geological  section  of  the  core  of  the  mountain.  A  considerable 
proportion  of  the  tunnel  is  now  bricked  over,  and  only  in  the  manholes, 
every  250  feet,  can  the  rock  be  seen;  and  secondly,  the  covering  of  soot 
and  smoke  on  the  rock  is  very  thick,  making  it  necessary  to  get  fresh  sur- 
faces by  hammering.     The  difficulties  of  working  by  lamplight  in  the  smoke 


70  GREEN  MOUFTAIlSrS  OF  MASSACHUSETTS. 

of  passing  trains  are  also  considerable.  Moreover,  that  part  ot  the  tun- 
nel wliich  would  have  afforded  the  most  important  contact  for  determining 
the  relations  of  the  Stockbridge  limestone  to  the  Hoosac  mountain  rocks  is 
entirely  bricked  over;  it  lies  in  the  decomposed  rock  which  caused  so  much 
trouble  during  the  building  of  the  tunnel.  Therefore,  while  the  general 
distribution  of  the  rocks  is  easily  found  in  the  tunnel,  much  less  was  done 
in  the  way  of  determining  relations  by  contact  than  would  have  been  possi- 
ble under  more  favorable  conditions. 

In  the  following  description  the  reader  is  referred  to  Profile  in,  PI.  v. 

Starting  at  the  west  end  of  the  tunnel  we  find  the  Stockbridge  lime- 
stone of  Hoosic  valle}^  in  the  long  open  cut  which  leads  to  the  tunnel 
mouth,  and  passing  under  the  masonry  of  the  portal ;  the  dip  alternates  in 
a  series  of  small  folds,  sometimes  east,  sometimes  west.  From  the  portal 
for  2,700  feet  the  tunnel  is  bricked,  but  at  several  of  the  manholes  we  find 
rock  in  place.  At  a  little  over  1,600  feet  we  find  in  a  manhole  the  first 
'occurrence  of  the  fine-grained  variety  of  gneiss  with  small  porphyritic  feld- 
spars, and  the  same  rock  again  at  about  1,900  feet  in.  Near  2,000  feet  the 
albite-schist  (Hoosac  schist)  is  found  in  all  of  the  manholes  to  about  3,800 
feet.  Then  by  transitional  rocks  this  passes  into  the  white  gneisses  which 
extend  to  6,000  feet,  where  by  gradual  transition  they  pass  into  the  coarse 
granitoid  gneiss;  this  rock  runs  as  far  as  10,500  feet,  then  after  250  feet  of 
bricking  the  conglomerate-gneiss  is  found  at  10,770  feet,  and  this  extends 
to  12,100  feet,  where  the  albite-schist  series  is  found  in  conformable  con- 
tact with  the  conglomerate-gneiss.  The  albite-schist,  succeeded  by  the 
Rowe  schist,  is  then  found  through  the  rest  of  the  tunnel.  We  find  then 
in  the  tunnel,  going  in  from  the  west:  first  the  limestone,  which  extends 
into  the  tunnel  proper  a  short  distance,  but  is  now  entirely  bricked  in; 
then  the  fine  grained,  banded,  white  gneiss  (Vermont  formation),  extending 
to  about  2,000  feet  from  the  portal;  then  the  albite-schist  for  1,750  feet; 
next  the  white  gneiss  (conglomerate-gneiss)  series  (Vermont)  for  a  little 
over  2,000  feet;  then  the  granitoid  gneiss  (Stamford gneiss)  for  a  little  over 
4,000  feet;  then  white  gneiss-conglomerate  for  1,500  feet;  and  the  schist 
formation  (Hoosac  schist  overlaid  by  Rowe  schist)  for  the  rest  of  the  way, 
or  about  12,900  feet,  of  which  the  last  6,000  is  occupied  by  the  gi-eenish 
sericitic  or  chloritic  Rowe  schist. 


TT  S.G>:ni,OGIGAJ-  SUHATTi'. 


MONOOnATU  5XIIL  pl.t: 


GEOLOGICU^  PROFILES   0¥   HOOSAC  MT. 

EAST- WEST     PROFILES. 


\. Northern  Section    Hoosac  Mi 


H.Section  from  Natural  Bridge  through  Schist  ndge 


W •:^LJ'ortat, 


Wh  6n        Schist.        iVhife    Gn  Granitoid  Gnoiss         Can^hmeratS  AlbitB    Sc/iist. 

IS.. Hoosac  Tunnel  ant^  Hoosac  Mi. 


ffar\-e  Schist 


W.  Sect/on  running  upl^t  CreekS  of  Tunrrel  Line 
to  Spruce  Hill. 


"    Buttress 

TJ.^Sect/on  through  Buttressto  crest  Hoosac  Mt. 


Hoosac  Mt 


<S5 


'W.  Section  across  Hoosac  Mt  throu_gh  contact  on  Pond. 


Clint  set         Conform 
Within  20  ft      Gorjtaei 

^m.Sect/on  up  51^  CreekS.  of  Buttress. 


VilL,  Bowen's  Creek  Section. 


Lineof  Tunnel   Spruce  Hill  Contact     Contact 


Horizontal  and  Vertical  Scale  3000  ft  =  Imch 

\      \      Limestone    (Stockbrid^e) 

□     Rowe  Schist 

IZZl     Albite  Sciiist  (Hoosac  Schist) 

I     1     White  Pnelss  quartzite  conglomerate 

■"■  (Vermont  Formation) 

[     I     Granitoid  Gneiss  (Stamford Gneiss) 

I       Pitch  ofaxes- 

The  sections  are  arranged  in  meridian. 

LONGITUDINAL   OR    NORTH      SOUTH    PROFILES. 


Tunnei643oftfromWPortai  'S.. LonPitudinal section  Hoosac  Mt.  from  Bowen's  Creek 

at  about  W contact  Granitoid  Gneiss 

and  Conglomerate.  tO    line  of   TuOnel. 


^.r^:^^^      " 


'Xl.SrN  section  through  end  synclinal 
"canoe"point  Hoosac  Mt. 


'^.NrS.measured  Stadia  Section  from  contact  Granitoid 
Gneiss  and  Conglomerate  to  Spruce  Hill  Fla^ 

With  dip  of 20'  thickness  Con^iomerate    740  ft 

"     -   "IS"       ■'  "  600 n. 


IKK. Section   through  extreme  length  Granitoid  Gneiss. 


A  HOf-Na.  CO  UTH  aMTO.MD. 


HOOSAC  MOUNTAIN.  71 

As  regards  the  structm-al  observations  it  was  not  practicable  to  attempt 
these  in  detail;  in  the  first  or  westerly  band  of  white  gneiss,  found  only  in 
manholes,  both  east  and  west  dips  were  observed,  and  no  contact  was  seen 
with  the  next  rock — the  albite  schist. 

This  next  band,  the  albite-schist,  has  in  general  an  easterly  dip,  but 
towards  the  contact  with  the  next  band  of  white  gneiss  has  a  very  steep  dip 
varying  from  east  to  west.  There  is  a  conformable  contact  and  transition 
between  the  two  r<:)cks. 

In  the  next  band  of  white  gneiss  dips  were  noted  varying  from  steep 
east  to  west:  the  observations  are  put  down  in  the  section.  At  about  6,000 
feet  the  rock  becomes  coarser  in  character,  corresponding  to  the  white 
gneisses,  transitional  to  the  granitoid;  it  contains  frequent  round  jjebbles  of 
blue  quartz,  corresponding  to  the  conglomerate  found  in  the  dumps  of  the 
tunnel.  From  here  for  about  700  feet  we  have  transitions  to  the  coarse 
gneiss;  lenses  or  layers  of  fine-grained  g-neiss  are  frequently  seen.  Nearly 
a  whole  day  was  spent  here  in  searching  for  a  contact,  by  careful  hammer- 
ing, but  none  could  be  found;  there  is  an  evident  transition,  as  observed 
elsewhere  at  points  outside  the  tunnel. 

The  area  of  the  coarse  granitoid  gneiss  contains  rock  of  an  even  char- 
acter; whatever  structure  exists  by  arrangement  of  mica  planes,  etc., 
remains  flat  or  gently  rolling  east  and  west.  The  east  contact  between  this 
I'ock  and  the  conglomerate-g'ueiss  is  concealed  by  the  brickwork. 

This  east  band  of  the  conglomerate-gneiss,  as  on  the  surface,  is  char- 
acterized by  a  steady,  well-marked  easterly  dijj  of  20°  to  30°,  and  this 
ends  very  near  the  central  shaft,  where  the  rock  is  overlain  by  the  albite- 
schist;  its  thickness  is  accordingly  about  600  feet,  which  agrees  closely 
with  that  found  on  the  surface.  The  structural  planes  of  the  two  rocks  are 
absolutely  conformable,  both  dipping  east  about  25°.  The  line  of  contact 
is  easily  found ;  witlun  a  few  inches  of  rock  they  pass  into  each  other  with- 
out a  break.  From  here  through  the  rest  of  the  tunnel  only  the  albite- 
schist,  passing  in  the  last  6,000  feet  into  fine-grained  greenish  schists,  is 
found.  The  dip  of  the  structural  planes  is  always  steep  east.  The  rock 
varies  in  character  as  on  the  surface,  in  color,  coarseness,  amount  of  albite, 
quartz  lenses,  etc. 

The  main  facts  then  brought  out  in  the  tunnel  are  that  there  is  a,  large 


72  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

central  mass  of  coarse  granitoid  gneiss  (Stamford  gneiss)  forming  the  core 
of  Hoosac  mountain;  that  this  is  flanked  on  either  side  by  a  band  of  tlie 
white  gneiss-conglomerate  (Vermont  formation),  the  eastern  band  having  a 
steady  east  dip  and  conformably  overlain  by  the  albite-schist  series,  the 
western  band  being  broader,  with  varying  dips  passing  by  gradual  transitions 
into  the  coarse  gneiss,  and  bounded  on  the  west  by  a  narrow  band  of  the 
albite-schist  (Hoosac  schist) ;  the  contact  between  the  two  rocks  being  con- 
formable and  transitional.  The  schist  bandis  succeeded  on  the  west  by  another 
band  of  fine-grained  white  gneiss  (Vermont)  and  this  in  turn  by  limestone 
(Stockl)ridge),  no  contacts  being  observed.  We  shall  speak  of  this  anti- 
clinal structure  further,  after  describing  the  geology  of  the  surface  of  the 
mountain. 

THE  REGION  EMBRACING  THE  CENTRAL  PART  OF  HOOSAC  MOUNTAIN. 

The  map  shows  the  distribution  of  the  formations  in  this  area.  The 
central  part,  forming  the  crest  of  the  mountain,  is  occupied  by  a  long  irreg- 
ularly oval  area  of  the  granitoid  gneiss,  the  long  axis  of  which  runs  nearly 
north  and  south  parallel  to  the  trend  of  the  mountain,  with  a  length  of  6 
miles  and  a  width  at  one  place  of  1^  miles.  This  is  surrounded  by  a  zone 
of  the  Avhite  gneiss  series  (Vermont)  about  one-half  mile  wide,  which  at 
the  southern  end  of  the  granitoid  gneiss  core  expands  into  a  broad  area  of 
white  gneiss-quartzite,  extending  down  to  the  southern  border  of  the  map. 
To  the  east,  the  great  expanse  of  the  albite-schists  (Hoosac  schist)  borders 
the  zone  of  the  white  gneiss-conglomerate,  running  in  an  almost  straight  line 
along  the  whole  eastern  edge  of  that  formation  to  the  southern  edge  of  the 
sheet.  It  circles  around  this  formation  to  the  north,  forming  the  surface 
rock  in  the  whole  northern  part  of  the  Hoosac  mountain,  and  sends  a  long 
narrow  tongue  down  on  the  west  side  of  the  white  gneiss  zone,  which  bends 
around  with  this  at  the  southern  end  of  the  granitoid  gneiss  area,  and 
.becomes  gradually  thinner  until  it  can  be  only  doubtfully  traced  by  loose 
blocks  at  the  extreme  point  of  the  curve. 

Lying  west  of  this  tongue  of  Hoosac  schist  we  have  another  area  of 
fine  grained  white  gneisses  or  quartzites,  with  a  vai-iable  width,  which  dis- 
appear under  the  drift  a  little  north  of  the  tunnel,  and  at  the  south  join 
the  great  mass  of  white  gneiss  at  the  southern  end. 


HOOSAC  MOUNTAIN, 


73 


Finally  the  limestone  borders  this  last  area  on  the  west.  The  relations 
of  these  rocks — granitoid  gneiss,  white  gneiss,  and  metamorphic  conglom- 
erate— are  best  shown  at  the  extreme  northern  end  of  the  area  of  the  first 
rock  (see  Profile  ix,  PL  v)  on  the  crest  of  Hoosac  mountain.  The  granitoid 
gneiss  is  here  of  the  typical  variety,  with  bright  blue  quartz  and  a  structure 
well  marked  in  the  mass.  This  dips  about  10°  to  15°  a  little  east  of  north. 
In  a  little  north  and  south  cleft,  just  south  of  a  small  swamp,  we  find  this 
rock  in  contact  with  the  overlying  conglomerate  gneiss.  Fig.  27  shows 
this.     The  series  dips  20°  in  a  direction  north  25°  east.     The  lower  part 


Fig.  27. — Contact  of  granitoid  gneiss  (Stamford  gneiss)  and  metamorpliic  conglomerate  (Vermont  formation).  Top  of 
Hoosac  mountain.    S(»utli  at  Spruce  liill. 

The  contact  runs  from  the  left  band  lower  corner  to  the  right  hand  upper  corner.  This  conglomerate  is  also  shown 
in  Fig.  15.    Notice  that  the  lines  of  structure  of  the  gneiss  follow  conformably  those  of  the  conglomerate. 

of  the  exposui'e  is  formed  of  typical  granitoid  gneiss.  Upon  this  the 
lower  beds  of  the  white  gneiss-conglomerate  rest  conformably.  In  the  latter 
rock  it  is  apparent  at  once  that  crushing  has  largely  affected  the  form  of  the 
pebbles.  To  this  cause  their  flattened  character  and  truncation  by  oblique 
planes  of  mica  is  undoubtedly  due,  and  yet  they  are  in  large  part  pebbles. 
Not  only  their  general  shape,  but  the  lithological  distinctness  shows  this. 
They  are  composed  either  of  massive  white  quartz,  or  blue  quartz,  or  smoky 
quartz,  or  in  some  cases  of  a  white  granulite,  or  lastly  of  a  fine  gi'ained  white 


74  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

gneiss  containing  blue  quartz  and  biotite.  In  one  large  pebble  the  gneissoid 
structure  in  it  is  quite  oblique.  It  is  easy  to  see  that  this  conformity  of  con- 
tact in  these  two  rocks,  both  of  which  have  so  much  secondary  structure 
developed  in  connection  with  crushing,  may  be  due  to  the  crushing  itself 
From  this  contact  northward  the  crest  of  Hoosac  mountain  makes  a  sharj) 
rise  in  a  series  of  bluffs  facing  south,  the  top  of  each  bluff  sloping  gently 
to  the  north.  Profiles  A  and  b,  PI.  xi,  show  this  feature  well.  In  PL  xi,  b, 
we  are  looking  west;  in  the  hollow  at  the  extreme  left  is  the  contact 
spoken  of,  and  the  white  gneiss-conglomerate  extends  to  a  point  shown 
about  the  middle  of  the  picture,  and  is  then  succeeded  by  the  albite-schist. 
The  gentle  northerly  dip  of  the  whole  series  can  easily  be  seen  by  the 
slope  of  all  the  steps  of  the  crest  to  the  north  (right).  See  also  PI.  v, 
Profile  IX.  Stalling  from  the  granitoid  gneiss  at  the  base  we  find  a 
thickness  of  600  to  700  feet  of  this  white  gneiss  conglomerate  with  a  very 
steady  northerly  dip  of  15°  to  20°.  At  the  base  the  rock  is  quite  coarse,  as 
pre^'iously  described.  As  we  ascend  in  the  series  it  becomes  gradually  finer 
grained.  The  granulite-gneiss  pebbles  become  smaller  and  smaller  and  are 
more  frequently  crossed  by  the  mica  of  the  groundmass;  the  quartz  pebbles, 
and  especially  those  of  blue  quartz,  preserve  their  rounded  character.  Fig. 
20  (from  a  large  cliff  of  this  medium  grained  rock)  shows  this  character 
finely;  the  large  pebbles  are  mainly  of  blue  quartz^  As  we  go  higher  up 
the  rock  becomes  more  and  more  even  grained  until  we  get  a  finely  banded 
muscovite-biotite-gneiss.  In  many  places  the  conglomerate  is  finely  crum- 
pled or  fluted,  the  axis  of  these  foldings  gently  inclined,  parallel  to  dip.  PI. 
X,  B,  shows  this  character;  here  the  flattened  lenticular  masses  we  call  pebbles 
are  themselves  gently  folded  with  the  rest  of  the  rock.  At  the  top  of  the 
conglomerate  this  rock  is  overlain  conformablv  by  the  Hoosac  albite-schis. 
series.  At  a  distance  of  half  a  foot  from  the  latter,  thin  bands  of  extremely 
garnetiferous  Hoosac  schist  alternate  with  bands  of  the  fine  grained  con- 
glomerates, forming  a  well  marked  transition.  The  rock  at  the  base  of 
the  Hoosac  schist  group  is  extremely  garnetiferous  and  of  a  dark,  almost 
black,  dense  character,  with  little  feldspar.  This  garnetiferous  character  at 
contact  with  the  white  gneiss  is  almost  constant  in  this  region  and  seems  to 
extend  some  distance  above  the  contact,  perhaps  50  or  100  feet;  in  the  space 


HOOSAC  MOUKTAIN.  75 

covered  by  our  Profile  ix,  PI.  v,  (which  is  plotted  from  a  stadia  section, 
checked  by  triangulation)  it  will  be  seen  that  there  is  nearly  800  feet  of  the 
albite-schist  to  the  summit  of  Spruce  hill,  where  the  section  stops.  The 
schist  preserves  its  gentle  northerly  dip  throughout,  with  a  quite  uniform 
character,  often  very  rich  in  the  albite  crystals. 

The  profile  we  have  just  described  gives  us  the  key  and  starting  point 
for  the  geology  of  Hoosac  mountain.  As  will  be  seen  later,  this  profile  is 
taken  at  the  northern  end  of  the  overturned  anticlinal  axis  of  Hoosac  moun- 
tain, tlie  whole  axis  having  this  gentle  pitch  or  plunge  to  the  north  which 
causes  the  dip  of  15°  to  20°  northerly.  The  granitoid  gneiss  disappears 
at  the  surface  here  and  is  found  again  in  the  center  of  the  Hoosac  tunnel 
in  the  same  meridian  line,  but  1,400  feet  lower  in  level.  Although  the  north- 
erly pitch  of  the  axis  has  here  brought  the  to])  of  the  arch  of  the  granitoid 
gneiss  far  below  the  surface,  enough  of  the  arch  remains  above  the  tunnel 
to  allow  a  length  of  sevei'al  thousand  feet  of  the  excavation  to  lie  in  this 
rock.     (See  Profile  x,  PI.  v.) 

Now  going  back  to  the  contact  of  granitoid  gneiss  and  gneiss-con- 
glomerate at  the  south  end  of  Profile  ix,  PI.  v,  and  tracing  the  contact  of 
the  two  rocks  westward,  in  a  few  hundred  feet  we  come  to  the  extreme  west 
prest  of  Hoosac  mountain  overlooking  the  valley  (see  PI.  iv).  Here  we  find 
the  continuation  of  the  two  rocks  in  contact  again  with  the  same  strike  and 
dip.  The  granitoid  gneiss  runs  a  hundred  yards  north  and  then  disappears; 
the  white  gneiss-conglomerate  makes  a  sharp  turn  over  the  prong  of  the  other 
rock  and  comes  in  on  the  west  side  of  it,  on  the  slope  of  the  mountain;  the 
white  gneiss  strikes  north  40°  east  and  dips  50°  west,  instead  of  striking  north 
67°  west  and  dipping  northeast.  The  manner  in  which  one  rock  mantles 
over  the  other  can  be  seen  very  plainly;  at  the  turn  they  are  within  20 
feet  of  each  other.  The  successive  outcrops  of  the  white  gneiss  on  lines 
radiating  out  from  this  point  of  the  turn  show  the  same  curving  around  of 
the  outcrops  from  a  northwest  to  a  northeast  strike. 

Following  in  the  same  way  the  top  of  the  conglomerate  towards  the 
west,  we  find  it  strikes  northwest  until  the  extreme  west  crest  of  the  moun- 
tain is  reached,  closely  overlain  by  the  Hoosac  schist;  the  outcrops  then 
suddenly  turn  and  descend  the  slope  of  the  mountain  obliquely  in  a  north- 


76  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

west  direction,  followed  closely  by  the  overlying  schist.  The  rocks  here  are 
very  much  crampled;  the  axes  of  the  crumplings  have  a  steady  direction 
about  north  10°  east  and  a  gentle  northerly  inclination  of  10°  to  15°, 
while  the  actual  line  of  outcrop  runs  northwest  down  the  mountain.  In  this 
way  the  schist  mantles  over  the  conglomerate  and  follows  it  down;  grad- 
ually the  line  of  outcrops  turns  and  runs  nearly  straight  down  the  moun- 
tain until  the  extreme  point  is  reached  nearly  half  way  down  to  the  valley. 
Here  we  find  the  gneiss  striking  north  10°  east  and  pitching  10°  to  15° 
northerly,  very  much  crumpled,  and  passing  under  a  cliff  of  the  schist  like- 
wise crumpled.  The  two  rocks  are  here  again  connected  by  transitional 
layers  in  which  bands  of  white  gneiss  alternate  with  bands  of  schist,  and 
the  gneiss  contains  a  great  abundance  of  the  porphyiitic  feldspars;  the 
schist  is  also  the  dark  garnetiferous  variety.  At  this  point  the  same  change 
of  position  previously  described  occurs,  namely  by  a  sudden  turn,  which 
can  be  traced  by  connected  outcrops;  the  scliist  comes  in  on  the  west  side 
of  the  white  gneiss  with  a  strike  north  10°  east,  a  strong  northerly  pitch, 
and  a  dip  of  the  foliation  (very  much  crumpled)  generally  steep  west. 
The  reader  is  referred  to  the  map  (PI.  iv)  for  the  graphic  presentation  of  these 
facts  J  the  outcrops  have  been  carefully  traced  step  by  step  and  important 
points  located  by  placing  flags  in  the  trees  and  putting  in  the  points  by  the 
plane  table.  Note  how  closely  the  apices  of  the  turn  in  the  granitoid  gneiss 
and  white  gneiss  coincide,  showing  the  conformity  of  the  series.  After  the 
rocks  have  made  this  turn  so  that  the  overlying  formations  come  to  lie  suc- 
cessively west  of  one  another,  there  is  no  difficulty  in  tracing  their  course 
to  the  south  along  the  side  of  the  mountain.  From  the  turn  in  the  contact 
between  granitoid  gneiss  and  white  gneiss-conglomerate,  the  line  of  contact 
runs  obliquely  down  the  mountain  in  a  south  by  west  direction  for  about  2 
miles,  where  it  reaches  its  lowest  point  topographically;  the  actual  contact 
has  not  been  found,  although  the  two  rocks  commonly  come  close  together, 
but  talus  from  the  granitoid  gneiss  conceals  the  contact.  The  white  gneiss 
often  forms  a  flat  bench  100  or  200  feet  wide.  The  structure  of  the  white 
gneiss,  as  mentioned  before,  dips  very  steeply  west  just  after  the  turn; 
within  a  quarter  of  a  mile  it  is  found  to  dip  near  the  contact  with  the  gran- 
itoid gently  east,  from  10°  to  25°;  but  commonly  the  i*ock  is  greatly  crum- 


HOOSAC  MOUNTAIN.  77 

pled,  the  axis  of  the  crumples  running  noi-th  20°  east  and  having  a  strong 
northerly  pitch.     Profile  iv'',  PL  v,  shows  this  feature. 

In  the  same  way  the  contact  between  the  white  gneiss  and  the  band  of 
Hoosac  albite-schist  can  be  traced  south  from  the  point  where  we  left  it. 
Both  rocks  are  very  much  crumpled,  the  axis  of  the  crumples  striking  a 
little  east  of  north  and  strongly  inclined  to  the  north;  the  contact  can  be 
found  within  a  few  feet;  the  structure  of  the  two  rocks  in  the  large  cliffs 
can  be  seen  on  the  average  to  be  nearly  perpendicular  or  dipping  steep 
west.  The  schist  near  the  contact  is  the  dark  garnetiferous  variety  found 
at  the  base  of  that  rock  on  the  top  of  the  moimtain. 

As  will  be  seen  from  the  map  the  schist  forms  only  a  narrow  band, 
bordered  again  on  the  west  by  another  area  of  gneiss. 

We  will  now  take  up  the  relations  of  the  granitoid  gneiss  and  white 
gneiss-conglomerate  and  trace  them  around  from  the  point  where  they  were 
last  seen  at  the  tui'n.  As  said  above  the  line  runs  obliquely  down  the  moun- 
tain side,  the  structure  of  the  two  rocks  dipping  gently  east;  that  is  to  say, 
the  white  gneiss  dips  in  under  the  granitoid  instead  of  overlying  it.  Near 
what  is  marked  Southwick  creek  on  the  map  the  granitoid  gneiss  reaches 
its  most  westerly  extension  and  its  lowest  topographical  level,  and  from 
here  the  outcrops  begin  to  rise  and  to  turn  gradually  and  run  southeast. 
PI.  v.  Profile  VII,  which  runs  up  Southwick  creek,  shows  this  relation  well;  the 
white  gneiss  has  a  steady  flat  moderate  easterly  dip  carrying  it  under  the 
granitoid  gneiss.  At  about  this  point  we  notice  a  transition  from  the  white 
gneiss  to  the  granitoid;  the  white  gneisses  are  coarse  and  very  feldspathic, 
so  that  it  is  almost  impossible  to  find  any  definite  line  of  demarkation 
between  the  two  rocks.  Continuing  a  third  of  a  mile  south  from  Southwick 
creek  we  come  to  the  place  where  Profile  x,  PI.  v,  crosses  the  contact  of  the  two 
rocks.  The  actual  junction  of  the  two  rocks  is  found  here  in  so  far  as  there 
can  be  said  to  be  a  junction.  The  strike  is  north  40°  west  and  the  dip  15° 
east.  Within  a  hundred  feet  horizontal  the  rock  forms  a  transition  between 
the  coarse  typical  granitoid  gneiss  on  one  side  and  the  fine-grained  banded 
white  gneisses  on  the  other.  From  here  the  contact  tm'ns  and  ascends  the 
m6untain  rapidly,  the  coarse  transitional  gneiss  making  it  always  impos- 
sible to  find  any  exact  contact;  the  strike  is  north  25°  west  and  the  dip 


78  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

flat  east.  After  reaching  the  crest  of  the  mountain  the  Hne  of  contact  turns 
approximately  north  and  south  with  north  and  south  strike  of  the  structure 
of  both  rocks,  the  dip  of  the  structural  plane  is  rolling  and  often  is  west- 
erly. When  we  come  to  the  extreme  end  of  the  west  side  of  the  granitoid 
gneiss  area,  where  the  line  makes  a  sharp  turn  to  the  east,  we  find  well 
marked  in  both  rocks  and  in  the  transitional  forms  a  strike  nearly  due  east 
and  west  and  a  rather  gentle  northerly  dip  (strike  north  77°  to  85°  west 
dip  10°  northerly).  The  coarse  transitional  rocks  belonging  to  the  white 
gneiss  series  can  be  traced  to  the  round  spur  about  1  mile  north  of  Savoy 
Hollow,  where  by  a  sudden  crumpling  the  rocks  turn  around  to  a  north  to 
south  strike  and  an  easterly  dip  and  then  run  northward. 

If  we  go  liack  to  the  contact  of  the  two  rocks  first  described  (south  of 
Spruce  hill),  and  follow  it  east,  we  find  that  the  line  of  contact  preserves  its 
east  and  west  strike  for  half  a  mile  and  then  begins  to  turn  southerly.  The 
congloraei'ate  preserves  its  character  fairly  well  for  that  distance;  but  half  a 
mile  further  the  strike  is  about  north  and  south  or  north  10°  west,  showing 
considerable  vai'iations,  but  there  is  always  an  easterl}^  dip  of  20°.  The  line 
of  contact  here  turns  southerly  and  is  concealed  by  drift.  Half  a  mile  farther 
south  we  find  the  coarse  transitional  gneiss,  instead  of  the  conglomerate, 
striking  here  north  42°  west  and  dipping  45°  east.  For  three-quarters  of 
a  mile  this  rock  continues  until  we  come  to  the  shore  of  the  second  pond 
crossing-  Profile  v,  PI.  v.  Around  the  shores  of  this  pond  the  relations  of  the 
rocks  are  well  exposed.  On  the  west  shore  the  typical  granitoid  gneiss  occurs 
with  blue  quartz,  witli  a  north  to  south  strike  and  easterly  dip  of  the 
structure.  For  1,000  feet  east  of  here  we  have  a  series  of  outcrops,  partly 
in  the  water,  which  consist  of  the  coarse  transitional  gneiss,  often  contain- 
ing granulitic  lenses  that  resemble  the  pebbles  of  the  conglomerate. 
There  are  many  loose  outcrops  of  the  genuine  conglomerate  with  blue 
quartz,  granulite,  and  gneiss  pebbles,  which  make  it  very  probable  that 
ledges  of  this  rock  exist  here.  Half  way  across  the  pond  we  find  the  con- 
tact of  these  coarse  transitional  gneisses  with  the  Hoosac  albite-schist,  the 
latter  resting  on  the  gneiss  and  the  structure  of  the  two  rocks  absolutely 
conformable — strike  north  10°  east,  dip  25°  easterly.  The  schist  is  very 
garnetiferous,  as   usual    near   the   contact,   aud    covers   the    rest    of   the 


HOOSAC  MOUNTAIN.  79 

sheet  from  the  contact  east  to  the  Rowe  schist.  The  area  covered  by  these 
transitional  coarse  gneisses  therefore  occupies  the  geological  position  of  the 
conglomerate-gneiss,  a  fact  which  the  occm'rence  of  the  "loose  ledges"  of 
conglomerate  seems  to  confirm.  North  of  the  lake  the  continuation  of  this 
coarse  transitional  gneiss  is  found  at  intervals  with  the  same  strike  and  dip. 
From  here  for  2^  miles  south  the  place  which  should  be  occupied  by 
the  white  gneiss-conglomerate  is  covered  with  drift,  and  not  a  single  out- 
crop is  found.  The  albite-schist,  with  a  constant  north  to  south  strike, 
borders  on  the  east  and  the  granitoid  gneiss  on  the  west.  Opj^osite  the 
post-office  of  Savoy  Center  the  next  outcrop  is  found.  This  is  quite  con- 
glomeratic in  aspect,  with  round,  blue  quartz  or  granulite  pebbles,  and  a 
strike  north  15°  west  and  dip  45°  east.  Intervening  between  this  and  the 
typical  granitoid  gneiss  to  the  west  we  find  the  same  coarse  transitional 
gneiss,  with  somewhat  varying  strike  and  dip.  Continuing  south  from  this 
last  exposure,  on  the  road  leading  to  Savoy  hollow,  we  find  occasional 
outcrops  of  coarse  transitional  gneiss  with  the  same  nearh*  north  to  south 
strike  and  easterly  dip.  This  brings  us  about  to  the  extreme  point  of  the 
ai-ea  of  granitoid  gneiss  and  to  the  white  gneiss-conglomerate  band  fol- 
lowed around  from  the  west  side.  The  relations  of  the  rocks  at  this  point 
are  peculiar  and  deserve  a  special  description.  The  to])ography  here  is 
well  marked.  It  is  easily  seen  on  the  map  that  a  long  spur  runs  out  from 
tlie  pt)int  of  the  granitoid  gneiss  for  a  mile  and  more  toward  Savoy  hollow. 
This  spur  is  caused  by  the  meeting  of  the  white  gneisses  of  the  east  and 
west  areas,  those  on  the  east  coming  down  with  a  north  to  south  strike  and 
easterly  dip,  those  on  the  west  striking  across  with  a  nearly  east  to  west 
strike  and  northerly  dip.  We  find  on  the  spur  the  rocks  very  sharply 
crumpled,  representing  the  sudden  turn  of  strike  and  dip;  some  layers 
striking  east  and  west  can  be  traced  to  the  place  where  the-\'  curve  around 
and  run  southerly  with  a  steep  easterly  dip.  At  one  point  on  the  spur, 
about  a  mile  north  of  Savoy  hollow,  we  find  a  curious  curving  series  of 
outcrops  of  a  very  coarse  porphyritic  gneiss,  containing  large  rounded 
feldspar  crystals,  blue  quartz,  etc. — an  "Augen"  gneiss.  The  outcrops  on 
the  east  side  strike  north  5°  west  and  dip  about  vertically.  This  gradu- 
ally curves  around  to  an  east  and  west  strike  and  steep  southerly  dip,  then 


80  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

to  a  northwest  strike  and  nortlierl}'  dip — that  is,  the  layers  circle  around 
in  the  space  of  a  few  hundred  feet,  giving  a  canoe-shaped  fold.  The 
development  of  the  very  large  porphyritic  feldspars  just  in  the  turn  is  also 
significant.  In  short,  this  space,  so  marked  topographically,  is  the  place 
where  part  of  the  layers  of  the  white  gneiss  are  crumpled  and  pinched 
together  in  the  extreme  point  of  the  great  fold  which  we  have  been  describ- 
ing. It  Avill  be  seen  from  what  has  been  said  that  the  central  part  and 
crest  of  Hoosac  mountain  is  composed  of  a  great  anticlinal  fold  in  the  three 
members  of  the  series — granitoid  gneiss  (Stamford  gneiss),  metamorphic 
conglomerate  (Vermont  formation),  and  albite-schist  (Hoosac  schist) — and 
that  this  fold  has  a  pitch  or  inclination  of  its  axis  of  10°  to  15°  to  the 
northward,  while  the  western  side  has  been  pushed  in  under  or  overturned, 
this  overturn  continuing  into  the  southwestern  part.  The  beds  are  in 
inverted  order  on  the  west  and  southwest  sides;  in  normal  order  on  the 
north  and  east  sides.  By  reason  of  the  pitch  of  the  axis  the  same  rock 
occm-s  in  the  tunnel,  1  mile  north  of  the  last  appearance  of  the  granitoid 
gneiss  on  the  surface,  flanked  on  both  sides  by  the  conglomerate  and 
albite-schist;  these  two  formations  on  the  east  side  dipping  east,  overlying 
the  granitoid  gneiss  in  normal  order  On  the  west  we  find  the  same  transi- 
tions between  granitoid  gneiss  and  white  gneiss-conglomerate  that  were 
observed  on  the  surface,  and  a  nearly  vertical  structure.  Profiles  x  and 
XII,  PI.  V,  give  these  relations  graphically. 

The  belt  of  Hoosac  schist  which  is  seen  on  the  map  to  run  around 
the  central  gneiss  and  nearly  to  join  the  great  mass  of  schist  on  the  east, 
starts  off"  from  the  main  mass  as  a  bi'oad  tongue,  narrowing  rapidly  to  a 
small  constant  width.  At  various  points  its  top  and  bottom  contacts  with 
the  gneiss  on  either  side  have  been  observed.  Over  the  tunnel  this  schist 
can  not  be  found  in  definite  contact  with  the  western  gneiss;  on  the  con- 
trary, there  is  a  gradual  transition,  which  can  be  seen  in  the  outcrops  on 
the  slope  of  the  mountain  above  the  Avest  shaft.  We  hardly  find  here  in 
the  schist  what  we  can  call  a  dip  of  any  kind — simply  the  usual  fluting, 
with  the  strong  northerly  pitch  of  the  axes.  Following  the  band  down  to 
a  point  some  hundred  yards  north  of  Profile  iv^,  PI.  v,  we  find  here  the  east 
contact  of  the  schist  and  white  gneiss.      The  schist  is  very  garnetiferous,  as 


V  S   GEOLOGICAL  SURVEY 


MONOGRAPH  ZXm  PL,  VI. 


AHni\diCD  i;rK  a.MW.Mr 


HOOSAC  MOUNTAIN.  81 

elsewhere.  Both  rocks  have  their  structure  vertical  with  the  small  folds, 
pitching  10°  to  15°  northerly.  In  Profile  iv*,  PI.  v,  itself  we  get  another 
contact.  From  here  for  2^  miles  to  Profile  v,  PI.  v,  the  black  schist  is  con- 
cealed; then  outcrops  occur  with  easterly  dip;  east  and  west  contacts  with 
the  gneiss  are  concealed.  In  the  creek  of  Profile  vii,  PI.  v,  we  have  a  long 
series  of  outcrops  of  the  schist  with  the  easterly  contact  beautifully  shown, 
the  westerly  within  a  few  feet.  These  schists  are  extremely  crumpled,  as 
shown  by  the  quartz  lenses;  these  crumples  pitch  gently  northerly.  The 
rock  is  very  garnetiferous  near  the  eastern  contact  with  the  white  gneiss; 
in  other  places  feldspathic.  At  the  east  contact  we  have  the  white  gneiss 
dipping  20°  easterly;  it  is  a  white,  muscovitic  variety.  The  schist  layers  can 
be  seen  within  less  than  4  feet  of  strata  from  the  base  of  the  gneiss,  dipping 
gently  under  it;  intervening  ledges  are  covered  by  the  water  or  soil.  It 
indicates  perfect  conformity,  both  series  dipping  east.  After  forming  a 
series  of  cascades  over  this  schist  the  creek  runs  out  on  a  level  and  we 
find  here  the  rock  succeeded  by  outcrops  of  micaceous  quartzite  or  fine 
grained  gneiss,  with  same  strike  (north  10°  east)  and  dip  25°  east;  the  dis- 
tance covered  from  one  rock  to  the  other  is  25  feet  horizontally. 

For  half  a  mile  south  from  the  upper  contact  of  Profile  vii,  PI.  v,  it 
can  be  traced  very  closely  with  the  same  strike  and  gentle  easterly  di]^, 
the  contact  being  found  often  within  a  few  feet  and  the  structure  of  the  two 
rocks  being  conformable.  At  a  mile  from  this  contact  we  come  to  Profile  x, 
PI.  V.  Here  the  actual  contact  was  again  easily  found  in  the  rocky  cliff, 
both  white  gneiss  and  black  garnetiferous  schist  much  crumpled,  but  with  a 
general  easterly  dip  of  10°  to  15°.  The  strike  is  north  25°  to  30°  west 
and  the  small  crumples  pitch  northerly  10°  to  15°.  This  inclination  affects 
the  topography;  Fig.  10,  p.  43,  represents  this  spur,  in  which  the  gentle 
slope  towards  the  left  of  the  picture  (north)  is  due  to  the  pitch  of  the  rocks. 
The  lower  contact  is  not  found  here.  In  Profile  viii,  PI.  v,  we  have  this 
schist  again  outcropping,  but  neither  contact. 

A  mile  farther,  on  the  north  fork  of  Tophet  creek,  in  a  deep  gorge,  we 
find  fine  exposures  of  the  schist,  much  crumpled,  and  at  the  head  of  the 
gorge  its  contact  with  the  overlying  white  gneiss,  which  here  again  con- 
tains transitional  layers  of  micaceous  gneiss.     Both  strike  north  10°  west 

MON  XXIII 6 


82  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

and  dip  15°  easterly.  From  this  contact  the  line  of  the  two  rocks  is  easily 
followed  over  the  hills  to  the  south  fork  of  Tophet  creek,  1  mile.  Here,  after 
crossing  numerous  exposures  of  the  western  band  of  gneiss,  the  creek  falls 
over  cliffs  of  the  typical  albite-schist  with  same  strike  (north  10°  west),  and 
gentle  easterly  dip  under  the  overlying  white  gneiss,  with  which  it  is  con- 
nected by  transitional  beds  as  before.     The  schist  is  always  garnetiferous. 

From  here  for  half  a  mile  the  schist  can  only  be  traced  by  loose  pieces 
and  one  outcrop  until  we  reach  the  corner  of  the  mountain;  here  we  find 
it  again  in  place  and  the  contact  vrith  the  overlying  gneiss  is  within  2  feet 
of  strata.  Both  are  conformable  in  structure  and  strike  north  45°  west  dip- 
ping 25°  northerly.  Here  both  rocks  are  turning  to  assume  their  east  to 
west  strike  at  the  extreme  point  of  the  turn  (curve),  and  only  crumpled  out- 
crops of  schist  are  found,  as  is  usual  in  these  turns. 

Following  the  schist  east  one-half  mile  we  find  it  overlying  the  west- 
ern band  of  white  gneiss,  which  has  here  curved  around  so  as  to  lie  south; 
the  upper  contact  is  not  seen;  the  schist  is  garnetiferous  and  passes  into 
the  underlying  white  gneiss  by  micaceous  layers.  The  strike  is  north  75° 
east,  dip  25°  northerly,  and  one-quarter  mile  farther  east  cliffs  of  the  gar- 
netiferous schist  are  found  striking  east  and  west  and  dipping  20°  north, 
closely  and  conformably  underlain  by  the  southern  band  of  white  gneiss. 
From  here  for  a  mile  only  fragments  of  the  schist  are  found.  Within  a 
quarter  of  a  mile  of  the  extreme  turn  a  small  outcrop  of  feldspathic  schist, 
exposing  a  thickness  of  30  feet,  is  interstratified  with  the  iine-grained  gneiss; 
strike  north  40°  west,  dip  20°  north.  One-half  a  mile  farther  in  the  line  of 
the  strike  of  the  gneisses,  which  are  curving  at  the  extreme  point  from  an 
east  to  west  to  a  north  to  south  strike,  a  solitary  outcrop  of  garnetiferous 
and  feldspathic  schist  is  found,  with  a  vertical  dip  and  strike  north  10° 
east,  which  represents  probably  the  last  trace  of  this  tongue,  which  we 
have  followed  continuously  from  the  main  mass.  It  seems  to  be  squeezed 
out  in  the  folds  of  white  gneiss. 

We  come  now  to  the  band  of  gneiss  (Vermont  formation)  lying  west 
of  this  band  of  Hoosac  schist.  All  of  this  gneiss  follows  closely  the  schist 
around  to  the  extreme  southeast  point,  where  it  merges  into  the  great  area 
of  gneiss  in  the  southern  part  of  the  map.     The  gneiss  of  this  area  has  a 


HOOSAC  MOUNTAIN.  83 

uniform  and  peculiar  character;  it  belongs  to  the  fine  grained  porphyritic 
gneiss  already  described  and  has  a  tendency  to  pass  into  micaceous  quartz- 
ite  or  even  pure  quartzite. 

The  first  exposure  found  is  on  the  side  of  the  mountain  about  1  mile 
north  of  the  tunnel  line,  where  it  is  within  a  few  feet  of  the  albite-schist, 
which  here  extends  up  the  mountain.  Both  rocks  are  conformable,  strike 
north  30°  east,  dip  60°  east;  to  the  north  the  rock  is  covered  with  glacial 
drift,  so  that  it  is  uncertain  where  it  finally  disappears,  but  the  two  bands 
of  albite-schist  come  close  together  both  east  and  west  of  it.  This  rock 
shows  a  remarkable  tendency  to  disintegrate.  This  "rotten  gneiss"  caused 
great  expense  and  loss  of  time  in  building  the  western  part  of  the  tunnel. 
At  the  tunnel  line  outcrops  of  this  rock  are  found  on  the  surface  at  the 
west  shaft  and  on  the  mountain  above  for  over  100  feet,  when  they  are  suc- 
cseded  by  the  schist;  but  transitional  rocks  made  it  impossible  to  draw  a 
line.  Toward  the  west  edge  of  this  gneiss  band,  a  few  hundred  yards  north 
of  the  tunnel  line,  an  old  iron  mine  alongside  the  road  is  composed  of  a 
massive  quartzite  containing  masses  of  limonitic  iron  ore,  the  structure  of 
which  is  not  determinable.  This  gneiss  was  also  found  in  the  tunnel  at 
several  manholes,  and  in  the  creek  just  south  of  the  tunnel  line  we  find 
several  outcrops  of  this  rock  as  indicated  on  the  map,  all  striking  about 
north  20°  east  and  dipping  east  at  varying  angles.  Also  a  few  hundred 
yards  south  of  the  portal  of  the  tunnel  we  have  an  outcrop  the  strike  of 
which  would  carry  it  very  close  to  the  portal. 

When  we  come  to  the  sharp  little  hill  of  Profile  iv"  ("the  Buttress") 
we  have  fine  exposures  of  this  gneiss  (see  Plate  v).  It  is  plain,  from  this 
section,  that  in  this  band  of  gneiss  we  have  considerable  folding.  One 
sharp  anticlinal  is  plainly  shown  here  with  many  smaller  crumples.  There 
are  several  hundred  feet  of  covered  space  between  the  western  outcrop  of 
gneiss  and  easternmost  of  limestone,  but  the  contact  with  the  schist  is  very 
close.  The  folds  of  this  gneiss  have  a  strong  northerly  pitch  of  as  much 
as  10°  in  Profile  iv". 

From  Profile  iv''  for  1^  miles  to  Profile  vii  we  have  only  two  or  three 
scattering  outcrops  of  this  rock  (see  PI.  v).  At  Profile  vii  it  is  represented 
by  one  outcrop  of  micaceous  quartzite  closely  underlying  and  conformable 


84  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

to  the  overlying  schist;  strike  north  10°  east,  dip  30°  easterly.  Three- 
quarters  of  a  mile  south,  in  the  next  creek,  two  or  three  outcrops  of  mica- 
ceous feldspathic  quartzite  strike  north  10°  west,  dip  25°  east.  The  curve 
of  the  strike  has  begun  here. 

Broad  benches  strewn  with  glacial  drift  cover  this  rock  in  all  this 
part  of  the  mountain.  At  this  place,  opposite  the  north  part  of  the  town 
of  Adams,  the  line  of  junction  of  the  limestone  with  the  gneiss  band  seems 
to  make  a  curve  westward,  for  we  find  one  outcrop  of  this  gneiss  in 
a  small  quarry  near  Adams.  The  strike  is  north  10°  west,  dip  25°  east. 
A  few  hundred  yards  south,  in  the  creek  marked  Anthonys  creek,  we  get 
outcrops  of  a  similar  gneiss;  strike  north  8°  west,  dip  50°  easterly.  Below 
this  a  few  feet  we  find  a  series  of  outcrops  of  a  massive  micaceous  quartz- 
ite, the  bedding  of  which  dips  25°  to  30°  easterly  and  strikes  north  15° 
west.  A  little  lower  down  along  the  road  we  find  the  Stockbridge  lime- 
stone striking  north  15°  west,  dip  25°  east;  we  find  this  within  a  few  feet 
of  the  quartzite  along  the  road.  Then  in  the  bank  there  is  a  crumbly 
transitional  rock  between  the  limestone  and  quartzite,  so  that  the  Stock- 
bridge  limestone  and  this  quartzite  seems  to  form  the  same  rock,  and  the 
fine  grained  banded  gneiss  appears  to  overlie  the  quartzite. 

In  the  canyon  of  Tophet  creek  we  have  clifi"s  of  the  limestone  with 
varying  strike  and  dip.  Ascending  the  creek,  near  the  upper  edge  of  the 
canyon,  we  find  a  large  ledge  of  massive  vitreous  quartzite  which  strikes 
northwest  and  is  overlaid  by  large  loose  ledges  of  the  fine  grained  gneiss, 
striking  north  35°  west,  dip  east  50°.  Several  hundred  feet  along  the  strike 
south,  and  in  the  creek  bed  there  is  the  conformable  contact  of  a  small 
piece  of  massive  quartzite  overlaid  east  by  the  gneiss,  both  dipping  east 
and  striking  north  10°  west.  Still  farther  south  on  Tophet  creek,  near  the 
entrance  to  Bowens  creek,  there  are  extensive  ledges  of  the  fine  grained 
gneiss  striking  north  and  south  and  dipping  east.  It  is  therefore  evident 
that  this  rock,  underlain  to  the  west  by  a  massive  quartzite,  is  succeeded 
by  the  limestone,  and  that  the  limestone  and  quartzite  pass  into  each  other 
by  transitions.  In  the  canyon  of  Tophet  creek  this  contact  is  concealed; 
it  is  some  hundred  feet  from  the  quartzite  to  the  first  cliff'  of  limestone. 

I'or  2,000  feet  east  across  the  strike  from  the  fine  grained  gneiss  at  the 


HOOSAC  MOUNTAIN.  85 

entrance  of  Bowens  creek  into  Tophet  creek,  a  gently  sloping  bench  con- 
ceals all  outcrops;  then  in  Bowens  creek  we  have  Profile  viii  giving  us  a 
typical  section  through  this  band  of  gneiss,  the  rock  varying  between  a 
vitreous  quartzite,  micaceous  quartzite,  and  the  fine  grained  gneiss  typical 
of  this  area.  Above,  the  schist  and  then  the  eastern  gneiss  succeed  the 
first  mentioned  rocks.  As  will  be  seen  in  Profile  viii  the  rocks  have  a 
moderate  easterly  dip  with  few  variations. 

The  next  exposure  is  on  the  north  fork  of  Tophet  creek,  where  this 
series  begins  a  few  feet  below  the  lowest  outcrop  of  the  schist,  and  forms 
a  continuation  of  the  canyon  of  the  creek  for  over  half  a  mile;  the  rock 
makes  great  cliff's  and  bluff's  with  a  well  marked  strike  north  10°  west  and 
a  gentle  dip  of  10°  to  15°  east.  Rock  one  hundred  and  fifty  feet  thick  can 
be  seen;  the  south  fork  of  Tophet  creek  shows  the  same;  here  the  rocks 
are  much  more  quartzose — often  a  massive  quartzite — and  the  dips  are 
irregular,  in  some  cases  northerly. 

Just  below  the  junction  of  the  two  forks  of  Tophet  creek  the  water 
flows  around  the  north  end  of  an  elliptical  hill  (Burlingames  hill),  the  crest 
of  which  is  formed  by  a  large  outcrop  of  massive  vitreous  quartzite  which 
strikes  north  10°  east,  dips  25°  east.  At  the  north  end  of  the  hill  the  creek 
exposes  outcrops  of  rock  with  the  same  strike,  and  an  easterly  dip  of  15°,  in 
which  a  lenticular  mass  of  massive  quartzite  passes  into  a  dark  feldspathic 
biotite  schist  resembling  the  transitions  between  albite  schist  and  gneiss. 
The  quartzite  passes  laterally  as  well  as  vertically  into  the  schist,  showing 
the  sudden  transitions  of  which  these  rocks  are  capable.  We  have  a  broad 
drift- covered  area  extending  1 J  miles  from  the  outcrops  of  massive  quartzite 
on  this  hill  to  the  limestone  outcrops,  and  south  to  the  schist  in  Cheshire; 
an  area  which  contains  no  outcrops  whatever.  From  the  south  fork  of 
Tophet  creek  we  get  no  outcrops  of  this  band  of  gneiss  until  we  get  to 
the  "point"  of  the  mountain.  This  locality  is  a  large  "canoe;"  that  is, 
the  strata  turn  suddenly  from  a  north  and  south  strike  and  easterly  dip  to 
an  east  and  west  strike  with  northerly  dip.  We  have  described  the  schist 
band  and  the  manner  in  which  it  is  overlain  and  underlain  by  white  gneiss. 
The  underlying  white  gneisses  corresponding  to  this  western  band  occur  in 
great  cliff's  with  a  strike  north  40°  west  and  dip  15°  to  20°  north.     From 


86  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

their  base  to  the  base  of  the  schist  they  correspond  to  a  thickness  of  450 
feet  but  on  the  theory  of  duphcation  to  only  half  that  amount,  having  the 
fine-grained  banded  character  of  this  western  area  of  gneisses.  These  cliffs 
strike  along  east  with  the  same  strike  and  dip.  The  profile  of  Hoosac 
mountain  seen  from  a  distance  shows  plainly  the  step-like  series  of  ter- 
races, sloping  gently  northward,  which  correspond  to  these  beds  of  gneiss. 
(See  PI.  V,  Profile  xi.)  Following  this  band  of  white  gneiss  east,  at  about 
one-half  mile  from  the  point  of  the  mountain  the  strike  has  turned  to  north 
75°  east.  One-quarter  mile  farther  there  are  again  cliffs  of  this  rock  strik- 
ing nearly  east  and  west  and  dipping  nortli;  the  schist  overlies  here  again. 
Beyond  this  point  it  is  no  longer  possible  to  separate  this  band  of  gneiss 
from  that  band  nearest  the  gi-anitoid  gneiss;  they  merge  together,  after  the 
band  of  schist  has  thinned  out,  in  the  great  area  of  contorted  white  gneiss 
in  the  southern  part  of  the  field. 

NORTHERN    AND    EASTERN    SCHIST   AREA. 

It  will  be  seen  that  the  whole  northern  third  of  the  region,  and  a  broad 
strip  along  the  east,  is  occupied  by  the  albite  schist,  with  commonly  an 
easterly  dip  and  north  to  south  strike.  It  will  be  noticed  that  there  are 
changes  in  the  dip  to  the  north ;  on  the  line  of  the  axis  of  the  mountain  the 
dip  is  north,  but  there  is  in  general  great  uniformity,  as  there  is  in  the  case 
of  this  rock  in  the  tunnel.  Of  course  this  steady  dip  does  not  mean  a  true 
monocline,  but  rather  a  series  of  folds  overthrown  to  the  west  and  eroded. 
No  attempt  has  been  made  in  the  field  to  unravel  the  more  minute  details 
of  this  structure ;  this  was  done  only  in  important  places,  where  the  relations 
of  the  other  rocks  require  it.  It  is  also  possible  that  troughs  of  the  over- 
lying Rowe  schist  occur  in  this  northern  area,  but  the  facts  have  not  been 
definitely  ascertained.  The  quartz  lenses  and  layers,  so  abundant  in  the 
schist,  are  found  to  be  always  parallel  to  the  bedding  at  contacts  with  other 
rocks  of  the  series,  where  the  alternation  of  material  shows  which  is  the 
plane  of  stratification,  and  hence  these  lenses  can  be  provisionally  accepted 
as  indications  of  stratification  elsewhere,  when,  as  is  often  the  case,  the  rock 
has  a  marked  transverse  cleavage.'     In  the  vicinity  of  Spruce  hill  the  schist 

'On  the  Greylock  side  cleavage  lamination  and  stratification  in  the  schists  hare  been  carefully 
distinguished  by  Mr.  Dale. 


HOOSAC  MOUNTAIN.  87 

continues  for  some  distance  to  have  its  northerly  pitch,  but  small  folds  begin 
to  come  in,  as  for  instance  in  Profile  in,  PI.  v,  parallel  to  the  tunnel  line,  on 
the  west  summit  of  the  mountain,  where  a  small  syncline  exists.  Note  in 
this  profile  on  the  west  slope  of  the  mountain  how  the  dips  roll  from  east  to 
west  with  commonly  a  northerly  pitch.  It  is  characteristic  of  this  rock 
that  it  forms  gorges  and  waterfalls  along  the  side  of  the  mountain.  Hoosac 
mountain  presents  an  unbroken  wall  for  12  miles  in  Massachusetts,  extend- 
ing into  Vermont.  Profile  i,  PI.  v,  gives  one  of  the  best  sections  through 
the  schist;  it  extends  from  the  valley  to  the  summit  of  Hoosac  mountain  and 
shows  the  structure  here  by  an  almost  continuous  section.  On  the  slope  of 
the  mountain  proper,  the  rocks  have  a  gentle  easterly  dip,  while  at  the  base 
there  is  considerable  rolling.  On  top  of  the  mountain  there  is  again  a  gentle 
rolling  of  the  rocks. 

The  west  end  of  Profile  i  is  separated  by  a  shallow,  drift-covered 
depression  a  few  hundred  yards  wide  from  a  long  north  and  south  ridge  in 
the  valley  (see  map)  on  the  summit  and  sides  of  which  we  find  the  typical 
Hoosac  albite  schist,  often  very  garnetiferous,  extending  in  an  almost  straight 
line  to  near  the  western  portal  of  the  tunnel,  where  it  stops.  This  ridge  of 
schist  is  everywhere  separated  from  that  of  Hoosac  mountain  by  this  small, 
drift-covered  hollow,  so  that  we  have  only  the  lithological  identity  to  cor- 
relate by.  This  rock  is  succeeded  by  the  limestone  on  the  west  tlu-oughout 
its  extent.  Profile  ii,  PI.  v,  shows  the  relations  of  the  rocks  across  this 
ridge,  beginning  with  those  which  are  exposed  on  the  north  fork  of  the 
Hoosic  river  in  North  Adams.  The  Stockbridge  limestone  has  here  its  most 
northern  outcrop  in  Hoosic  valley  and  strikes  north  20°  east,  the  dip  varies 
considerably;  the  rock  is  much  folded,  a  fact  well  shown  in  a  quarrv  and 
chasm  in  the  limestone  at  the  "Natural  Bridge."  This  rock  is  succeeded 
within  60  feet  by  a  schist  with  conformable  strike,  and  dip  east  40°.  About 
800  feet  across  the  strike  east  from  this  contact,  with  one  or  two  intervening 
outcrops  of  schist,  we  have  a  high  bluff  along  the  river,  composed  of  mica- 
ceous schistose  limestone,  effervescing  strongly  with  acid,  striking  north  25° 
east  and  dipping  25°  east.  This  bluff  extends  for  some  distance  and  is  70 
feet  high,  exposing  a  considerable  thickness  of  the  rock.  At  the  top  of  the 
bluff  there  is  a  flat  bench,  gently  rising  to  the  east  (evidently  formed  by 


88  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

this  rock)  for  nearly  500  feet,  then  rising  more  steeply  to  the  summit  of 
this  ridge,  where  we  find  the  albite  schist  with  the  same  strike,  but  greatly 
cnimpled  dip.  There  are  no  outcrops  between  the  top  of  this  bluff  of  lime- 
stone and  the  schist,  about  3,000  feet  horizontally.  No  outcrops  are  found 
for  a  mile  south  of  this  place  along  the  strike,  then  we  find  the  limestone  in 
a  small  quaiTy,  striking  north  35°  east,  dip  35°  east.  This  limestone  at  the 
top  of  the  quarry  is  conformably  overlaid  by  a  black  schist,  and  50  feet  dis- 
tant across  the  strike  an  outcrop  of  the  typical  Hoosac  schist  has  the  same 
strike,  crumpled  in  small  folds  with  a  northerly  pitch.  It  looks  very  much 
like  a  transition  from  limestone  to  schist  at  these  places.  From  here  there 
are  few  outcrops  down  to  the  West  Portal,  where  the  schist  entnely  runs 
out  just  north  of  the  tunnel.  There  seems  to  be  in  this  ridge  a  trough  of 
schist  with  a  pretty  steady  north  to  south  strike  and  crumpled  dip.  The 
outcrops  can  be  traced  along  the  summit  of  the  ridge  almost  continuously. 
The  northern  area  of  schist  overlying  the  Vermont  conglomerate  south 
of  Spruce  hill  soon  turns  from  the  east  and  west  strike  as  we  go  east  to  the 
steady  north  and  south  strike  of  the  eastern  border,  and  runs  from  here  with 
an  almost  straight  line  to  the  southern  border  of  the  sheet.  The  conformable 
contact  with  the  white  gneiss  (Vermont)  at  the  pond  (Profile  v,  PI.  v) 
has  already  been  mentioned;  the  line  of  contact  runs  about  9  miles  to  a 
point  about  1  mile  northeast  of  Windsor  Hill,  where  the  contact  is  well 
shown  between  the  fine  grained  white  gneiss  and  the  schist;  strike  north 
20°  east,  dip  steep  east.  _ There  are  here  transitional  beds  between  the 
gneiss  and  schist  formed  by  very  micaceous  layers.  Over  a  mile  due  east 
of  Windsor  Hill  the  same  thing  occurs  again;  the  schists  are  here  very 
garnetiferous.  The  Rowe  schists,  which  lie  east  of  and  hence  overlie  the 
Hoosac  (albite)  schist,  have  been  mentioned  previously.  They .  appear 
on  the  map  (PI.  i)  as  a  narrow  strip  at  the  eastern  edge,  passing  into  the 
Hoosac  schist  at  the  line  of  contact.  They  will  be  described  in  their  more 
general  relations  in  a  forthcoming  memoir  of  Prof.  B.  K.  Emerson  covering 
the  territory  east  of  the  map. 

THE  REGION  SOUTH  OF  CHESHIRE  AND  OF  THE  HOOSIC  VALLEY. 

The  area  of  gneisses  (Vermont  formation)  south  and  southeast  of  the 
granitoid  gneiss  can  best  be  described  by  beginning  at  the  southwest  end. 


HOOSAC  MOUNTAIN.  89 

In  the  Hoosic  valley  here  we  have  the  Stockbridge  limestone  crossmg 
the  valley  from  the  Greylock  side  and  running  close  up  to  the  slope  of  the 
hills  on  the  east  side.  This  limestone  is  succeeded  by  a  broad  band  of 
quartzite  (Vermont)  on  the  slopes  of  the  hills  and  this  again  by  a  series  of 
gneisses  (Vermont)  which  extend  to  the  crest  and  back  from  it,  east.  In 
the  southwest  part  of  the  map  the  quartzite  occurs  in  a  long  ridge  running 
northerly  and  southerly,  just  east  of  the  Hoosic  river.  It  is  a  very  massive 
vitreous  variety,  the  dip  of  which  is  obscure.  A  little  hollow,  perhaps  a  hun- 
dred feet  wide,  separates  it  from  the  gneisses  on  the  east,  which  strike  north 
25°  east  parallel  to  the  trend  of  the  quartzite,  and  dip  first  west  then  east — 
much  folded.  Following  1  mile  north  from  here  without  finding  out- 
crops, we  come  to  a  creek  running  into  the  large  pond  in  the  valley  a  few 
hundred  yards  north  of  Berkshire  depot.  Just  where  this  creek  issues  from 
the  sloping  benches  a  little  east  of  the  road  we  find  well-marked  ledges  of 
the  limestone  striking  north  37°  east,  dip  steep  westerly;  125  feet  east  the 
next  outcrop  dips  east  65°  and  is  in  contact  conformably  with  a  calcareous 
quartzite;  for  one-half  mile  or  more  up  this  creek  beds  of  this  calcareous 
quartzite  are  found,  in  places  massive  quartzite;  then,  after  a  covered  inter- 
val of  400  feet,  we  find  ledges  of  laminated  gneiss  (quartzose)  dipping  also 
east  50°  (strike  north  40°  east);  farther  up  the  creek  this  gneiss  is  succeeded 
by  coarse  gneisses  with  blue  quartz  resembling  the  granitoid,  also  dipping 
east.  We  have  here  a  transition  of  the  Stockbridge  limestone  into  the  Ver- 
mont quartzite,  and  this  is  in  turn  overlain  by  gneisses,  the  whole  series 
inverted.  The  limestone  is  covered  along  the  contact  from  here  north  to 
Cheshire.  The  line  of  contact  between  quartzite  and  gneiss  can  be  easily 
followed  north  along  the  side  of  the  mountain,  the  two  rocks  never  quite 
in  contact,  until  we  reach  a  point  on  the  side  of  the  mountain  half  a 
mile  south  of  the  north  end  of  the  pond;  here  the  quartzite  and  underly- 
ing fine  grained  gneiss  make  a  sharp  turn,  and,  as  is  so  often  the  case  in 
this  region,  in  the  turn  the  rocks  are  not  eroded  away.  The  southernmost 
outcrop  of  a  laminated  quartzite  strikes  north  45°  east,  dips  60°  west;  across 
a  littl-e  ravine  to  the  north  this  curves  to  strike  east  and  west,  dip  50°  north- 
erly. It  is  overlain  by  a  large  bed  of  very  massive  vitreous  quartzite,  and 
near  the  outcrops  of  the  latter  numerous  angular  blocks  of  a  quartzite-brec- 
cia  cemented  by  limonite  occui- — a  rock  often  found  in  these  sharp  turns  in 


90  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

the  quartzite  and  connected  witli  the  crashing.  The  laminated  quartzite  is 
closely  underlain  by  curving  outcrops  of  a  rather  coarse  layer  gneiss,  in 
which  long  flat  bands  of  feldspathic  material,  blue  quartz,  and  biotite 
alternate.  This  again  is  conformably  underlain  by  outcrops  of  fine-grained 
biotite  gneiss.  These  outcrops  are  separated  a  few  feet  horizontally. 
Their  contacts  must  be  within  a  few  inches  of  strata,  and  tliey  are  perfectly 
conformable.  This  proves  the  structural  conformity  of  this  massive  quartzite 
series  with  the  underlying  gneisses.  A  mile  and  a  half  north  of  this  we 
find  the  sharp  point  of  the  mountain,  on  the  east  side  of  which  the  valley 
makes  a  bay  or  "cove"  running  a  mile  south.  This  "point"  of  the  moun- 
tain is  formed  by  the  massive  quartzite,  south  to  the  crest,  and  also  at  its 
north  and  west  base,  where  the  quartzite  is  quarried  for  sand,  and  the  stream 
makes  a  fine  cut  through  it.  One-eighth  mile  east  of  Cheshire  village  the 
quartzite  is  quarried  from  a  large  mass,  striking  north  30°  west,  dipping  20° 
northerly,  and  can  be  followed  southeast  for  at  least  one-quarter  of  a  mile 
with  the  same  strike  and  dip.  Along  the  west  side  of  this  point  of  the 
mountain  the  quartzite  has  been  quarried  in  several  places.  About  1  mile 
south  of  Cheshire,  near  the  north  end  of  the  pond,  at  a  sand  mine,  the 
quartzite  strikes  north  40°  to  50°  east,  dips  20°  west,  while  northeast  of  here, 
on  the  slopes  of  the  mountain,  near  another  old  sand-mine,  the  strike  is 
north  80°  west,  dip  20°  northerly.  Tliis  "point"  of  the  mountain  therefore 
represents  an  anticline  in  the  quartzite,  collapsed  and  overthrown  to  the 
east — a  prow,  <  »r  inverted  canoe.  On  the  top  of  the  crest  of  the  mountain 
the  quartzite  forms  the  slopes  and  highest  crests,  striking  north  15°  west, 
dip  15°  east;  in  the  east  slopes  it  strikes  north  30°  west,  dips  30°  east. 

Going  back  to  the  quartzite  quarry,  in  a  little  ravine  off"  the  road,  an 
outcrop  of  calcareous  quartzite  is  found  overlain  within  10  feet  by  an  im- 
pure limestone.  The  strike  is  about  north  20°  west,  dip  about  30°  north- 
east. A  few  hundred  yards  further  north  outcrops  of  limestone  are  found 
striking  north  50°  west,  dipping  45°  east.  It  is  to  be  noticed  therefore  that 
the  limestone  also  circles  around  the  quartzite  to  the  north  and  strikes  south 
to  lie  east  of  the  quartzite,  forming  in  part  at  least  the  bay  or  "cove"  of  the 
valley.  No  outcrop,  however,  of  the  limestone  in  place  is  found  in  this 
cove.     The  southern  rim  of  the  cove  is  formed  by  massive  quartzite  which 


HOOSAC  MOUNTAIN.  91 

strikes  north  85°  east,  dip  50°  northerly,  gradually  turning  on  both  sides 
of  the  cove  tp  a  north  and  south  strike.  Thus  on  the  east  side  of  the  cove 
it  strikes  north  65°  east  and  dips  west;  approaching  the  succeeding  point 
of  the  mountain  it  strikes  north  and  south,  then  at  the  extreme  of  this  point 
north  37°  west,  dij)  vertical.  The  extreme  point  is  formed  by  a  very  massive 
vitreous  quartzite,  150  yards  nortli  of  which  there  is  a  loose  outcrop  of  lime- 
stone, probably  not  in  place.  There  are  also  small  ledges  of  schist  on  the 
west  edge  of  the  cove  which  probably  are  in  place;  strike  north  32°  east, 
dip  west  steep.  They  show  that  the  schist  area  north  of  the  cove  runs  in 
here  near  the  quartzite.  As  we  go  east  from  this  second  point  the  quartzite 
strikes  north  30°  west,  dip  northeast,  then  begins  to  strike  east  and  west 
and  dip  northerly  with  a  constant  strike.  About  a  mile  from  this  second 
"point,"  or  sharp  canoe,  in  the  quartzite,  we  come  to  a  very  important  local- 
ity, where  this  massive  quartzite  and  conglomerate  passes  along  the  strike 
into  the  white  gneiss  series  of  Hoosac  mountain.  Half  a  mile  from  the 
second  "point"  the  massive  quartzite  runs  up  the  hill,  striking  north  80° 
east,  dip  northerly  80°.  A  great  thickness  of  massive  quartzite  is  exposed 
here ;  in  some  cases  there  are  beds  of  well-marked  conglomerate  with  quartz 
})ebbles;  this  quartzite  runs  in  great  cliffs  up  the  side  of  the  mountain  (see 
map,  PI.  i).  As  it  approaches  the  summit  it  becomes  more  and  more 
micaceous.  At  the  summit  and  near  the  north  to  south  road  running  to 
Windsor,  it  changes  along  the  strike  within  200  feet  into  a  fine-grained  white 
gneiss.  The  quartzite  on  this  hill  is  separated  into  two  divisions  by  a  layer 
of  black  biotite  schist  of  some  thickness  Tlie  rocks  turn  around  this  hill, 
which  represents  a  quartzite  dome  (the  rocks  dipping  north),  and  then  by 
their  dip  are  carried  down  to  DrA'  brook,  to  which  they  can  be  easily  traced 
by  long  cliffs  and  scattering  outcrops. 

This  brings  us  to  the  area  between  Dry  brook  on  the  south,  the  "point 
of  the  mountain"  north  (where  the  central  series  of  Hoosac  mountain 
makes  its  sliarp  turn  to  the  east),  and  the  western  border  of  the  Hoosac 
schists  on  the  east.  The  rocks  we  find  in  this  area  are  varieties  of  the 
white  gneiss,  often  coarse.  Along  tlie  western  border  there  are  quartzites 
and  conglomerates  interbanded  with  gneisses,  wliile  the  large  area  of  schist 
in  Hoosic  valley  extends  east  into  the  gneiss  area.  Three  general  pecu- 
liarities of  structure  may  be  noted  (see  map,  PI.  i) : 


92  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

First.  Ill  the  west  part  of  tlie  area,  between  Dry  brook  and  the  curve 
north  (about  2  miles  from  north  to  south  and  1  mile  wide),  there  is  a  quite 
steady  strike  about  north  50°  west  and  moderate  northerly  dip;  a  perfect 
monoclinal  structure. 

Second.  In  the  belt  east  of  this,  1  mile  or  more  wide  (on  the  map  the 
central  area  of  flat  summits),  the  gneisses  are  greatly  curved  and  twisted. 

Third.  In  the  belt  extending  from  the  previous  one  to  the  border  of 
the  schists  the  normal  north  to  south  strike  occurs  with  predominating  east- 
ern dips,  as  in  the  schists. 

This  east  and  west  strike  and  monoclinal  north  dip  was  a  matter  diffi- 
cult of  explanation,  as  there  appeared  to  be  a  great  series  of  gneisses  and 
quartzites,  thousands  of  feet  in  thickness,  underlying  the  series  of  the  north- 
ern part  of  Hoosac  mountain.  It  was  not  until  the  white  gneiss- conglom- 
erate and  schist  tongue  had  been  traced  around  the  core  of  the  gi'anitoid 
gneiss,  and  it  had  become  evident  that  there  was  an  underturn  of  these 
rocks,  and  that  they  were  really  geologically  above  the  granitoid  gneiss,  as 
in  their  normal  position  in  the  region  of  the  tunnel,  that  it  was  possible  to 
exjjlain  the  monoclinal  dip  of  the  gneisses  further  south.  It  is  now  believed 
that  this  is  due  to  a  series  of  east-west  transverse  crinkles,  pushed  under 
and  collapsed  from  the  south,  so  that  there  is  a  constant  duplication  of 
strata  in  an  apparent  conformable  series.  One  proof  of  this  theory  is  the 
fact  that  we  find  the  actual  connection  between  two  adjacent  layers  of  the 
monoclinal  series  in  several  cases  on  the  west  brow  of  the  mountain. 

Ill  one  case  a  band  of  the  gneiss  having  the  schist  both  north  and  south 
of  it  was  traced  continuously  along  the  strike  for  a  half  mile.  It  gradually 
turned  to  a  northerly  direction,  the  schist  closely  following,  and  then  came 
to  an  end,  the  gneiss  terminating  in  a  small  crumpled  outcrop  and  the  schist 
each  side  circling  around  and  joining.  The  zone  nearer  the  schist  on  the 
east,  with  general  north  and  south  strike  and  easterly  di]),  must  represent  a 
large  series  of  similar  north  and  south  folds  overturned  to  the  west,  and 
the  areas  of  extremely  crumpled  gneiss  between  the  two  represent  the 
turning  point  where  the  east  and  west  folds  ai'e  twisted  around  to  the  north 
and  south  direction. 

In  the  following  details  the  reader  should  refer  to  the  map  (PI.  i),  on 


HOOSAC  MOUNTAIN.  93 

which  the  observations  are  platted.  In  the  previous  descriptions  the  Ver- 
mont quartzite  had  been  followed  to  where  the  lower  part  passed  into  schist- 
ose quartzite  and  finally  into  banded  white  gneiss,  and  had  been  traced 
down  to  Dry  brook.  The  upper  layer  of  quartzite  also  is  carried  down  to 
Dry  brook  and  appears  in  massive  ledges  along  the  brook,  just  where  it 
issues  from  the  mountain.  It  is  quarried  here  in  a  sand  mine  and  runs  up 
the  brook  several  hundi-ed  feet  in  great  ledges,  striking  north  35°  west,  dip 
northeast  25°.  In  one  place,  a  few  feet  west  of  the  sand  mine,  the  quartzite 
forms  an  iron  breccia,  which  is  evidence  of  crushing.  From  the  sand  quarry 
this  quartzite  can  be  traced  along  the  strike  for  a  quarter  of  a  mile  into 
the  region  of  the  gneiss.  At  first  it  forms  a  massive  quartzite  in  bluffs ; 
then  bands  of  micaceous  gneiss  come  in;  and  there  are  alternating  layers  a 
foot  or  two  wide  of  pure  quartzite  and  layers  of  finely  banded  white  gneiss. 
These  changes  are  well  shown  in  this  distance.  The  transition  from  quartz- 
ite to  gneiss  is  unmistakable  and  plainly  to  be  followed.  There  are  ledges 
of  rock  here  which  have  elongated  pebbles  resembling  the  conglomerate. 
For  a  mile  north  we  have  a  series  of  fine-grained,  banded  white  gneisses, 
with  steady  strike  north  40°  to  50°  west  and  northerly  dip,  which  on  the 
west  slopes  of  the  mountain  towards  the  valley  are  greatly  contorted,  the 
layers  of  the  monocline  doubling  on  themselves  and  running  back  in  a 
manner  which  it  would  be  impossible  to  describe  in  detail. 

At  a  point  a  mile  north  of  Dry  brook,  just  on  the  west  edge  of  the 
mountain,  we  find  a  large  blufi"  of  gneissoid  conglomerate,  the  flattened 
pebbles  composed  of  quartz  grains,  while  muscovite  and  biotite  plates  and 
some  feldspar,  with  octahedra  of  magnetite  form  the  cement — a  gneiss. 
The  rock  is  often  banded,  bands  of  mica-schist  alternating  with  those  of 
conglomerate.  The  ledge  strikes  north  40°  west  and  dips  40°  northerly. 
The  continuation  of  this  series  of  rocks  can  be  traced  over  a  mile  southeast 
with  about  the  same  strike  and  dip.  This  bluff"  is  on  the  west  crest  of  the 
mountain.  When  we  go  north  from  this  outcrop  we  can  trace  this  series 
of  conglomerates  within  a  space  of  about  a  quarter  of  a  mile  to  outcrops 
with  northeast  strike  and  steep  northerly  dip,  then  east  and  west  strike  with 
northerly  dip,  and  then  the  same  oi'iginal  strike  north  40°  west,  dip  north- 
east, with  which  we  started;  the  rock  then  strikes  southeast  into  the  gneiss 


94  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

area  of  the  Hoosac  mountain,  where  its  character  is  lost.  Thus  we  have 
here  the  case  of  two  layers  of  the  monoclinal  series  joining  to  form  one 
double  band,  the  connection  made  by  a  series  of  curving  layers  at  the  west 
edge  of  the  mountain.  This  conglomerate  is  bounded  on  the  west  by  beds 
of  massive  quartzite  which  can  be  traced  by  loose  pieces  along  the  moun- 
tain side  nearly  to  Dry  brook,  where  they  connect  with  the  quartzite  of  the 
sand  quarry.  By  what  complicated  crumpling  this  is  effected  it  is  difficult 
to  say. 

In  the  httle  brook  running  west  down  the  side  of  the  mountain,  about 
midway  between  Dry  brook  and  the  turn  of  the  mountain,  we  have  an 
important  contact  between  the  schist  (forming  the  large  area  in  the  valley) 
and  the  (Vermont)  quartzite  of  the  side  of  the  mountain.  The  two  rocks 
are  conformable,  strike  north  35°  west,  dip  30°  northeast.  This  schist 
extends  north  to  the  turn  of  the  mountain,  there  running  in  east  among  the 
gneisses  for  some  distance;  it  is  impossible  to  describe  the  contoiiion  it  has 
undergone;  it  is  in  general  a  series  of  small  minor  folds  whose  axes  dip 
northerly  with  the  dip  of  the  strata.  The  line  of  outcrop  is  hence  very 
winding  and  iiregular.  In  places  just  here  the  schist  assumes  the  form  of  a 
massive  iron  schist  composed  of  quartz  grains,  magnetite,  graphite,  and 
biotite,  which  is  easily  followed.  About  half  a  mile  south  of  the  turn  it  will 
be  noticed  on  the  map  (PI.  i)  that  the  gneiss  (^'ermont)  sends  a  cur^^ng 
tongue  northward  surrounded  by  schist  on  either  side;  we  have  in  this 
another  good  proof  of  the  real  duplication  of  layers  which  causes  the  mono- 
clinal dip  of  the  gneisses.  The  schist  and  gneiss  are  conformable  and  follow 
each  other  closely  to  the  point  where  curATng  layers  of  schist  circle  around 
the  gneiss  and  cut  it  off.  ■  It  is  a  very  sharp  anticlinal  curve,  the  gneiss 
doubling  back  on  itself  wnth  the  schist  closely  following.     (See  p.  92.) 

In  a  small  brook  flowing  west  at  the  point  of  the  mountain,  just  below 
the  cross  roads  we  find  again  the  schist  in  conformable  contact  with  a 
quartzite  which  here  overlies  it.  Both  sti'ike  north  45°  east  and  dip  west 
gently.  A  few  hundred  feet  east  a  quartzite  white  gneiss  is  found  overly- 
ing the  black  modification  of  the  schist  mentioned  above,  which  can  be 
traced  along  in  bluffs  for  nearly  a  mile,  forming  the  base  of  the  western 
band  of  white  gneiss,  where  it  has  tmnied  to  mn  east.     About  a  mile  dis- 


HOOSAO  MOUNTAIN.  95 

tant  it  forms  locally  a  crumbly  quartzite  which  has  been  quarried;  in  the 
intervening-  space  we  have  the  same  phenomenon  of  transition  of  quartzite 
to  gneiss  described  before  near  Dry  brook;  that  is,  we  have  small  layers 
or  lenses  of  the  quai-tzite  in  the  gneiss. 

West  of  the  contact  of  schist  and  quartzite  under  the  bi'idge,  the  two 
rocks  extend  some  hundred  feet  downstream;  then  they  rise  together  to 
the  bluff's  and  run  into  the  open  meadows,  where  we  find  outcrops  of  biotite- 
gneiss  overlying  the  quartzite.  No  contact  with  the  quartzite  can  be  found, 
but  the  three  rocks  follow  one  another  in  several  sharp  turns,  in  which  they 
seem  to  conform  in  structure.  The  strike  turns  within  300  yards  from 
north  60*^  west,  with  northeast  dip,  to  north  45°  east,  with  westerly  dip. 
This  can-ies  the  rock  down  southeast  to  an  outcrop  along  the  road,  where 
we  have  in  place  a  large  ledge  of  the  quartzite-breccia  indicating  a  sharp 
turn.  Some  hundred  feet  northeast  an  outcrop  of  the  quartzite  strikes 
north  and  south,  dipping  east.  These  outcrops  are  scattering,  and  from 
this  point  north  we  have  a  large  drift-covered  area  with  no  outcrop  what- 
ever (see  map,  PI.  i).  They  are  mentioned  in  detail  because  they  occur 
in  the  south  end  of  the  hill  in  which  "Burlingames"  massive  quartzite  is 
found,  about  half  a  mile  distant,  and  it  seems  probable  that  this  is  the  same 
quartzite  very  much  crurnpled  (corresponding  to  the  "canoe"  in  which  all 
the  rocks  here  are  folded).  This  enables  us  to  connect  it  with  "Burlin- 
game's"  quartzite  and  with  the  line  of  quartzite  observed  at  intervals  all  the 
way  south  from  the  tunnel  line. 

We  have  heretofore  been  dealing  with  the  boundaries  of  the  great  area 
of  (Vermont)  gneisses  and  quartzites  between  the  Stockbridge  limestone  on 
the  west,  the  Hoosac  schists  on  the  east,  and  the  granitoid  gneiss  (Stamford 
gneiss)  on  the  north,  covering  on  the  map  parts  of  Windsor,  Dalton,  and 
Savoy.  The  attempt  has  not  been  made  to  determine  in  detail  the  structure 
of  the  interior  of  this  mass,  although  a  glance  at  the  numerous  observations 
on  the  map  will  show  that  the  ground  has  been  fairly  well  covered.  It  is 
impossible,  so  far  as  our  work  has  gone,  to  recognize  definite  horizons  within 
this  mass,  and  without  these  it  would  be  hopeless  to  trace  out  the  exact 
structural  features. 

It  was  mentioned,  in  speaking  of  the  contact  of  the  Vermont  quartzite 


96  GREEN  MOUlvlTAlNS  IN  MASSACHUSETTS. 

and  Stockbridg-e  limestone,  that  the  quartzite  was  succeeded  by  gneisses 
with  conformable  strike  and  easterly  dip,  which  are  often  quite  coarse, 
with  blue  quartz,  resembling  the  granitoid  gneiss.  This  feature  can  be 
noticed  at  several  places;  for  instance,  east  of  the  exposure  of  quartzite 
at  the  extreme  south  end  of  the  map.  We  go  east  for  nearly  a  mile,  find- 
ing gneisses,  part  coarse,  part  fine,  and  then  come  to  massive  quartzite, 
and  well-marked  conglomerate  (not  metamorphic  gneiss-conglomerate),  with 
pebbles  of  blue,  white,  and  black  quartz.  The  quartzite  also  circles  around 
the  eastern  part  of  this  area  in  Dalton  (south  of  the  limits  of  this  map), 
where  it  is  again  associated  with  limestone.  We  find  rather  contorted 
gneisses  in  the  central  part  of  this  area,  under  the  word  "Dalton"  on  the 
map,  and  farther  north  massive  quartzite  with  north  and  south  strike  and 
varying  dip,  which  is  the  southern  continuation  of  that  forming  the  sharp 
quartzite  "points"  of  the  mountain  in  Cheshire.  So  this  part  is  evidentl}" 
composed  of  numerous  north  to  south  troughs  of  the  quartzite  and  conglom- 
erate, with  areas  of  the  underlying  gneiss,  the  quartzite  covering  the  gneiss 
at  both  ends  and  being  folded  under  it  on  the  west. 

This  statement  is  also  true  of  an  area  running  south  from  the  second 
point  of  the  mountain,  where  the  rocks  are  quartzite,  quai'tz-schist,  and 
quartzose  gneisses,  with  beds  of  quartzite-conglomerate,  the  strike  being 
north  and  south  and  dip  steadily  east. 

In  the  region  directly  south  of  Dry  brook  we  have  coarse  gneisses  with 
blue  quartz,  underlying  the  fine  grained  quartzose  gneisses  (Vermont)  which 
represent  the  quartzites,  and  therefore  perhaps  correspond  to  the  granitoid 
gneiss  (Stamford  gneiss)  of  the  central  part  of  Hoosac  mountain. 

In  Windsor  we  have  the  same  series  of  white  gneisses,  the  conglomerate 
character  not  marked,  it  being  probably  too  far  east,  and  the  increasing 
metamorphism  having  perhaps  masked  the  original  characters. 

A  large  part  of  this  area  is  very  poor  in  outcrops,  being  flat  and  drift- 
covered.  We  have  therefore  described  this  large  region  principally  in 
reference  to  its  boimdaries,  where  by  the  contact  with  other  rocks  the  true 
relations  and  structure  can  be  determined,  and  we  hope  that  our  observations 
establish — first,  the  conformity  of  the  Stockbridge  limestone  and  Vermont 
quartzite,  the  latter  underlying  when  in  the  normal  position,  as  is  shown  by 
the  contacts  and  lithological  passage  and  the  fact  that  the  limestone  is  sharply 


HOOSAO  MOUNTAIN.  97 

folded  with  the  quartzite;  second,  the  identity  of  the  quartzite-conglom- 
erate  horizon  underlying  the  limestone  (that  is,  the  Vermont  quartzite)  with 
the  fine  grained  white  gneisses  of  the  Dalton- Windsor  area,  and  of  these 
with  the  white  gneiss  series  of  the  central  mass  of  Hoosac  mountain ;  third, 
the  conformable  contacts  of  the  schist  area  in  Hoosic  valley  with  members 
of  the  quartzite-white-gneiss  series. 

HOOSIC   VALLEY   SCHIST. 

We  have  still  to  take  up  the  relations  of  this  large  schist  area  to  the 
limestone.  This  rock  is  a  typical  schist,  often  garnetiferous,  coming  in  places 
close  to  the  quartzite — at  the  "cove"  within  250  yards.  Near  the  quartzite 
tongue  on  the  western  side  of  the  "cove"  we  find  the  ground  filled  with 
loose  pieces  of  limestone  and  schist,  with  beautiful  transitions  between 
the  two  rocks  caused  by  the  presence  of  the  twinned  plagioclases  of 
the  schist  in  the  limestone  (see  p.  64).  It  may  be  mentioned  that  the 
same  rocks  occur  in  the  beds  of  Mount  Greylock.  Only  loose  pieces  of 
this  transitional  material  occur  here,  with  one  exception,  but  as  they  are 
nearly  on  the  line  of  contact  of  limestone  and  schist  it  can  fairly  be  pre- 
sumed that  they  are  nearly  in  place  and  represent  direct  contact;  one  ledge 
alone  is  exactly  in  place.  The  contacts  of  this  schist  with  the  quartzites  of 
the  white  gneiss  series  have  been  mentioned;  in  one  case  the  schist  under- 
lies, in  the  other  overlies.  In  the  former  case,  near  the  large  "canoe,"  we 
know  that  the  white  gneiss  series  is  inverted;  in  the  other  we  know  that  it 
must  be  normal,  and  hence  the  position  of  the  schist  as  overlying  the 
quartzite-gneiss  is  made  clear.  The  Stockbridge  limestone  bounds  this  schist 
on  the  west  and  northwest.  At  the  southwest  corner  no  contact  is  found, 
although  the  two  rocks  come  quite  close  together,  the  schist  forming  a  hill, 
the  limestone  lying  in  the  valley  at  its  base.  The  contact  (concealed)  runs 
along  to  Cheshire  Harbor,  where  limestone  and  schist  are  within  20  feet 
horizontally.  The  two  rocks  have  the  same  strike,  north  35°  east.  The 
dip  of  the  limestone  is  30°  westerly;  that  of  the  schist  is  obscure,  but 
appears  to  be  westerly.  This  seems,  therefore,  to  be  a  conformable  juxta- 
position, although  actual  contact  is  wanting.  The  line  of  contact  runs 
north  for  a  mile,  then  doubles  around  the  north  ridge  of  the  schist  and  runs 

MON  XXIII 7 


98  GEEBN  MOUNTAINS  IN  MASSACHUSETTS. 

southeast.  Where  it  crosses  Dry  brook  we  fiud  massive  hmestone  within 
a  few  feet  of  the  schist,  and  the  hmestone  seems  to  dip  under  the  schist. 
There  is  also  exposed  in  the  brook,  near  the  contact,  interbanded  hme- 
stone and  schist  near  the  contact  of  both  rocks,  just  as  observed  in  North 
Adams  (see  p.  88).  The  hne  of  contact  just  here  is  very  irregular,  zigzag- 
ging, as  we  should  expect  in  these  crumpled,  sharply  folded  rocks.  At 
the  south  end  of  the  lenticular  hill  north  of  Dry  brook  the  outcrops  disap- 
pear for  over  a  mile,  when  we  come  to  Tophet  brook,  where  we  have  the 
gneiss,  quartzite,  and  limestone  in  close  contact,  as  previously  described. 
From  here  north  to  the  locality  in  North  Adams  descril^ed  (p.  88)  the 
contact  of  the  limestone  is  concealed  on  the  east,  although  in  places  very 
close.  The  structure  is  given  on  the  map  (PI.  i  and  iv)  by  strikes 
and  dips.  North  of  the  North  Adams  locality  no  limestone  in  place  has 
been  discovered.  The  head  of  the  valley  containing  the  north  fork  of  the 
Hoosic  river,  some  8  or  9  miles  from  North  Adams,  is  formed  by  the 
schists  of  the  northern  part  of  Hoosac  mountain.  The  limestone  evidently 
runs  up  for  some  distance  from  North  Adams,  covered  with  drift,  and  then 
disappears. 

THE   REGION   AROUND    CLARKSBURG    MOUNTAIN   AND    STAMFORD,  VERMONT. 

This  brings  us  to  the  last  area  to  be  described  in  this  report,  namely, 
the  mass  of  Clarksburg  jnountain,  northeast  of  Williamstown  and  northwest 
of  North  Adams.  As  will  be  seen  by  the  map,  the  north  and  south  forks 
of  Hoosic  river  unite  at  North  Adams  and  flow  due  west  through  an  east  to 
west  valley,  lying  between  the  north  end  of  the  Greylock  mass  and  the 
south  slopes  of  a  high  mountain  mass  extending  down  from  Stamford,  Ver- 
mont, into  the  town  of  Clarksburg,  Massachusetts. 

We  find  the  Stockbridge  limestone  in  the  streets  of  North  Adams  (see 
map,  PI.  i)  and  in  the  high  ridge  just  south  of  the  railroad,  where  it  is  found 
in  contact  with  and  overlying  the  Mount  Greylock  Berkshire  schist.  The 
latter  rock  is  cut  through  by  a  raih'oad  tunnel  just  west  of  the  North  Adams 
depot,  where  the  limestone  forms  part  of  the  eastern  side  of  the  Greylock 
synclinorium,  really  underlying  the  Berkshire  schist,  but  here  inverted  by 
a  sharp,  overturned  fold. 


HOOSAC  MOUNTAIN.  99 

The  summit  of  Clarksburg-  mountain  is  composed  of  a  mass  of  granitoid 
gneiss  (Stamford  gneiss)  identical  in  petrographic  characters  with  that  of 
the  Hoosac  tunnel  (Stamford  granite).  This  is  overlain  by  the  Clarksburg 
quartzite  (Vermont  formation)  on  the  west  and  south  sides,  and  by  quartzites 
and  gneisses  on  the  east  side,  the  contacts  having  been  found.  In  this 
quartzite  Mr.  Walcott  has  found  the  remains  of  trilobites,  making  it  Lower 
Cambrian,  and  we  sliall  now  endeavor  to  show  thnt  this  is  represented  by 
the  gneiss  found  on  the  east  side  of  the  mountain. 

Near  the  old  signal  station  on  Clarksburg  mountain  the  quartzite  is 
represented  at  the  immediate  contact  by  a  blue  quartz  pebble  conglomerate, 
quite  micaceous,  the  pebbles  composed  of  aggregate  quartz.  Some  distance 
ab(3ve  the  contact  the  quartzite  contains  beds  of  a  quartz  schist  of  consid- 
erable thickness.  The  quartzite  and  conglomerate  are  found  within  2  or  3 
feet  of  strata  of  each  other,  the  quartzite  striking  on  the  average  about  north 
33°  west,  and  dipping  25°  southwest.  The  granitoid  gneiss  in  part  has 
little  structure,  but  in  several  places  this  feature  is  well  marked  by  the  mica 
planes,  which  are  in  general  parallel  both  in  strike  and  dip  to  those  of  the 
quai-tzite,  so  that  in  so  far  as  we  can  accept  as  stratification  such  structui-al 
planes  in  the  gneiss,  the  two  rocks  are  parallel.  From  this  place,  on  the 
northwest  edge  of  the  mountain,  the  line  of  contact,  curving  gently,  runs  to 
the  southeast  brow  of  the  mountain  above  North  Adams,  where  it  turns 
and  strikes  northeast.  The  contact  here  between  the  two  rocks  is  very 
close,  and  the  stmcture  of  the  granitoid  gneiss  obscure.  The  rock  is  massive. 
The  quartzite  strikes  north  30°  east,  dips  40°  southeast.  The  line  of  contact 
across  the  mountain  can  be  traced  in  a  general  ^^''ay,  but  no  outcrops  near 
together  have  been  found. 

The  whole  south  slope  of  the  mountain  down  to  the  valley  is  covered 
with  the  quartzite  and  the  intei'banded  quartz  schist.  The  southwest  dip  is 
well  marked  above  Williamstown,  while  on  the  North  Adams  side  it  is  south- 
east. This  mountain  is  a  large  quartzite  dome,  doubtless  with  many  minor 
crumples.  This  quartzite  is  found  as  low  down  as  the  river  bank  opposite 
the  cemetery  in  North  Adams.  It  is  last  seen  in  contact  with  the  granitoid 
gneiss  at  the  place  mentioned  above,  but  it  is  thence  eroded  away  to  the 
north  for  a  distance  of  2|  miles,  in  which  drift  covers  the  valley  and  lower 
slopes  of  the  mountain,  the  granitoid  gneiss  occupying  the  crest. 


100 


GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 


Just  north  of  the  Massachusetts  state  line,  in  Vermont,  about  2  J  miles 
northeast  of  the  last  contact,  we  find  again  the  contact  of  the  granitoid  gneiss 
with  quartzite;  this  is  in  Stamford,  in  the  liills  west  of  the  village.^ 

The  gi-anitoid  gneiss  has  the  same  general  characters  that  it  has  further 
south.  The  contact  is  found  near  an  old  schoolhouse  along  the  roadside. 
The  quartzite  is  micaceous  and  strikes  north  30°  to  55°  east,  bemg  curved 
a  little  in  the  outcrop  and  dipping  42°  east;  the  contact  is  seen  here  within 


Fig.  28.— Contact  of  granitoid  gueias  (Stamford  gneiss)  and  quartzite  (Vermont  formation),  Stamford,  Vt.  Looking 
nortli. 

Tlie  gneisa  tills  the  left  half  of  the  figure.  It  is  here  very  coarse,  with  structure  feebly  indicated.  The  hollow  in 
its  center  (through  which  the  road  goes)  is  caused  by  the  erosion  of  a  vertical  dike  of  amphibolite  about  11  feet  wide, 
which  does  not  penetrate  the  (xuartzite.     The  quartzite  is  seen  on  the  right,  dipping  southeast. 

1  foot  of  strata,  and  by  digging  the  actual  contact  was  found.  The  lamina- 
tion of  the  granitoid  gneiss  strikes  north  55°  east,  dips  about  40°  easterly; 
that  is,  in  a  general  way  conformable  to  the  Ijedding  of  the  quartzite.  At 
this  place  a  vertical  band  of  rock  14  feet  wide  strikes  north  60°  west,  or 
across  the  strike  of  l^oth  rocks;  it  has  the  character  of  the  altered  rocks 
described  on  pages  65  to  69  and  is  undoubtedly  a  dike;  this  runs  in  a 
straight  line  through  the  granitoid  gneiss,  but  abuts  against  the  quartzite 


'  C.  H.  Hitchcock  briefly  describea  this  locality  in  Geology  of  Vermont,  p.  601. 


HOOSAC  MOUNTAIN 


101 


without  passing  into  it,  and  the  quartzite  has  a  curious  thickening  of  its 
layers  where  the  dike  joins  it,  as  though  there  had  been  a  hoUow,  owing  to 
erosion  of  the  dike  before  deposition  of  quartzite.  It  seems  therefore  to 
show  the  most  perfect  unconformity  between  the  granitoid  gneiss  and  the 
overlying  quartzite,  although  the  lines  of  structure  of  both  rocks  are  parallel. 
(See  Figs.  28  and  29.)  We  can  trace  this  contact  northward  for  a  quarter  of 
a  mile  or  more;  the  quartzite  is  interbanded  with  very  feldspathic  gneisses, 
the  whole  forming  quite  a  thick  series.     The  rocks  dip  east  (43°  east,  strike 


Fig.  29. — Contact  of  granitoid  gneiss  and  quartzite;  same  locality  as  28,  looking  east,  showing  the  quartzite  nearer. 
Tlie  dike  was  foi^nd,  by  digging,  to  lie  against  the  quartzite  without  passing  into  it,  and  the  quartzite  shows  a  curi- 
ous lenticular  thickening  just  in  the  line  of  the  dike,  as  though  there  had  been  a  depression  there  at  the  time  of  deposit. 

north  40°  east)  and  so  does  the  structure  of  the  granitoid  gneiss.  Between 
this  point  and  the  quartzite  above  Noi'th  Adams  one  outcrop  of  quartzite 
conglomerate  has  been  found  in  place,  strike  north  45°  east,  dip  30°  east. 
There  seems  therefore  no  doubt  that  this  series  of  quartzites  and  gneisses, 
lying  on  the  granitoid  gneiss  without  a  fault,  are  the  same  as  the  quartzite 
at  North  Adams,  2  miles  off:  they  have  the  same  strike  and  dip  and  lie 
on  the  same  rock,  and  a  glance  at  the  map  will  show  that  the  line  of  strike 
runs  from  one  to  the  other.     We  have  here  then  the  second  proof  that  the 


102  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

white  gneiss-cong-lomerate  of  Hoosac  mountain  is  the  Cambrian  quartzite 
(Vermont). 

GENERAL  CONCLUSIONS. 

In  the  previous  pages  a  presentation  of  the  facts  observed  has  been 
attempted  without  drawing  conclusions  or  stating  results.  A  brief  sum- 
mary is  therefore  hei'e  introduced. 

The  rocks  of  Hoosac  niountain  consist  of  quartzites,  conglomerates, 
gneisses,  limestones,  schists,  and  amphibolites.  In  all  these  rocks  there  is 
abundant  evidence  that  some  elements  have  been  crushed  b}-  great  pres- 
sure; the  large  broken  microcline  and  quartz  masses  of  tlie  coarse  gneiss 
and  the  pebbles  of  the  conglomerate  show  this,  and  this  crushing  has 
been  accompanied  by  chemical  action  which  has  formed  new  feldspar,  mica, 
and  quartz.  With  the  exception  of  the  pebbles  of  the  conglomerates,  it  is 
with  great  difficulty  that  we  recognize  the  remains  of  detrital  material,  and 
yet  a  large  part  of  the  series  is  of  detrital  origin.  The  rocks  as  we  now 
find  them  are  thoroughly  metamorphic,  and  yet  we  feel  sure,  that  the 
material  for  the  present  rocks  must  have  come  from  the  old  sediments.  To 
trace  the  process  of  change  is  a  problem  of  the  future.  If,  as  tliis  work  indi- 
cates, these  rocks  are  simply  the  Cambrian  and  Silurian  sandstones,  lime- 
stones, and  shales,  altered  by  a  metamorphism  inci'easing  from  the  Hudson 
river  eastward,  then  careful  petrographic  studies  along  an  east  to  west 
line  ought  to  solve  this  problem.  A  partial  investigation  of  some  of  the 
rocks  of  Mount  Greylock,  made  by  the  writer,  shows  the  great  similarity 
between  the  metamorphic  rocks  of  Hoosac  mountain  and  of  Grreylock, 
qualitatively  considered,  but  in  quantity  jhe  difference  is  striking.  There 
are  no  coarse  gneisses  on  Greylock,  and  it  is  only  locally  that  fine-grained 
banded  gneisses  are  found,  but  limestones,  quartzites,  and  schists  (or  phyl- 
lites)  abound,  and  we  must  again  state  the  absolute  lithologic  identity  of 
these  varieties  with  those  of  Hoosac.  The  schists  of  Mount  Greylock  and  of 
the  Taconic  range  have  the  same  crystals  of  albite  and  the  same  ottrelite ;  the 
limestone  of  Greylock  is  feldspathic,  just  like  that  at  the  base  of  Hoosac.  It 
is  then  a  suggestion  worth  considering  whether  the  metamorphism  does  not 
increase  as  we  go  downward  as  Avell  as  eastward.  The  schists  of  Greylock 
and  those  of  Hoosac  at  the  top  of  the  series  are  alike;  the  coarse  gneisses 


HOOSAC  MOUNTAIN.  103 

at  the  base  of  the  Hoosac  series  are  not  found  in  Mount  Greylock  or  in 
the  Taconic  range,  at  least  not  here.  I  am  not  pre})ared  to  say  that  the  gran- 
itoid gneiss  itself  might  not  be  an  altered  sediment,  instead  of  an  eruptive 
granite  affected  by  dynamic  metamorphisra,  but  in  such  an  extreme  case 
we  need  careful  proof  of  the  process  of  change,  which  we  can  not  yet  give. 
This  rock  has  perhaps  rightly  been  called  Archean  by  J.  D.  Dana,  C.  H. 
Hitchcock,  C.  D.  Walcott,  and  others,  the  proof  resting  on  some  litho- 
logical  resemblance  or  on  unconformity  with  the  overlying  rock.  It  has 
been  shown  in  the  previous  pages  that  this  evidence  is  unsatisfactory,  for 
the  most  absolute  conformity  exists  in  places,  and  the  overlying  rocks  some- 
times take  on  the  characters  of  the  granitoid  gneiss.  The  altered  trap  dike 
found  in  Stamford,  which  cuts  the  granitoid  gneiss  but  not  the  quartzite,  is 
the  first  conclusive  evidence  of  nonconformity. 

Another  striking  fact  is  the  uniform  result  produced  by  metamor- 
phism  in  the  originally  dissimilar  rocks.  The  amphibolites  were  primarily 
trap  rocks  composed  of  hornblende  and  feldspar,  and  even  the  hornblende 
may  have  been  derived  from  augite  and  the  rock  a  diabase ;  but  this  fact, 
proved  for  rocks  in  other  regions,  is  yet  in  doubt  here.  By  the  metamor- 
phism  of  these  eruptive  rocks  new  feldspar,  biotite,  hornblende,  etc.,  are 
formed — of  which  minerals  some  occur  with  the  same  peculiar  features 
(feldspar)  in  the  schists  which  have  been  formed  from  sediments  (shales, 
slates,  etc.).  In  the  process  of  metamorphism  here  there  must  have  been 
an  important  chemical  action  originating  from  without  the  rocks. 

A  further  unexplained  condition  i^  the  vertical  position  of  the  plane 
of  lithologic  change  toward  a  gneissic  character.  The  fossiliferous  Cam- 
brian quartzite  (Vermont)  of  Clarksburg  mountain  forms  a  great  dome,  on 
the  east  side  of  which  it  strikes  northeast  toward  the  crystalline  rocks,  and 
within  2  miles,  in  Stamford,  Vt.,  we  find  it  partially  changed  to  gneisses. 
The  quartzite  of  Cheshire  preserves  its  character  as  quartzite  until  its  strike 
carries  it  east  across  a  certain  meridian  (the  west  crest  of  Hoosac  moun- 
tain), then  in  a  quarter  of  a  mile,  passing  this  line,  it  gradually  changes 
into  a  white  gneiss  by  taking  up  feldspar  and  mica.  A  mile  or  so  nortli  we 
find  that  the  ends  of  the  little  cross-crinkles  in  the  white  gneiss  nortli  of 
Dry  brook  are  quartzite  and  ordinary  quartzite-conglomerate.  They  pass 
into  white  gneiss  when  they  strike  east  within  a  very  short  distance. 


104  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

Lastly,  there  is  the  limestone  wliicli  on  Greylock  underlies  and  is  inter- 
stratified  with  the  schists;  we  find  this  In  Hoosic  valley  close  to  the  gneiss 
and  quartzites,  but  no  sign  of  it  on  the  mountain  proper.  Reviewing  the 
evidence  bearing  on  the  position  of  the  limestone,  we  have  on  Hoosac  moun- 
tain a  conformable  series — granitoid  gneiss,  overlain  by  a  white-gneiss-con- 
glomerate-quartzite  formation,  and  this  by  schist.  We  trace  along  the  strike 
the  quartzite  of  Hoosic  valley  into  tlij?  white  gneiss-conglomerate-quartzite 
series  underlying  the  schists;  and  we  also  trace  the  same  Cambrian  quartzite 
of  Clarksburg  mountain  into  white  gneisses.  This  quartzite  of  Hoosic  val- 
ley we  find  in  several  localities  passing  upward  into  the  limestone;  it  is  Prof. 
Dana's  quartz  rock  which  underlies  the  limestone.  This  quartzite  we  trace 
also  laterally  into  the  Hoosac  mountain  white  gneisses,  and  we  find  the  schist 
which  borders  the  limestone  of  Hoosic  valley  in  several  confonnable  con- 
tacts with  the  mountain  quartzites  and  white  gneisses  with  no  intervening 
limestone.  We  find  near  the  contact  of  schist  and  limestone  perfect  trans- 
itional feldspathic  micaceous  limestones  (not  all  in  place)  and  near  North 
Adams  very  close  proximity  of  the  schist  belonging  to  Hoosac  mountain  with 
limestone.  There  seeems  to  be  conformity  between  all  the  rocks,  and  yet 
the  limestone  is  wanting  in  the  mountain  section.  The  only  solution  would 
seem  to  be  that  the  limestone  is  replaced  by  the  schist  on  the  other  side  of 
the  line  or  plane  mentioned  above,  whether  it  be  an  original  shore  line,  or 
some  bounding  line  or  plane  of  certain  conditions  of  metamorphism  peculiar 
to  the  axis  of  the  Green  mountains.  To  bring  in  a  fault  or  tlu'ust  plane  at 
the  base  of  the  Hoosac  mountain,  cutting  off  the  crystalline  rocks  of  the 
Green  mountains  from  the  fossiliferous  rocks  west,  is  an  easy  solution  of  a 
difficult  problem,  l)ut  not  the  correct  one  if  the  facts  are  correctly  inter- 
preted.^ 

There  remain  to  summarize  the  facts  bearing  on  the  stratigraphy  of 
Hoosac  mountain.  The  reasons  for  the  conclusions  as  to  the  general  struc- 
ture of  Hoosac  mountain  need  not  be  recapitulated  here ;  it  is  an  anticlinal 
fold,  the  axis  of  which  lies  nearly  in  the  meridian.  This  axis  is  not  horizontal, 
but  inclines  or  "pitches"  (to  borrow  a  term  used  for  similar  folds  in  the  New 

'  The  reader  is  referred  to  Part  i  for  a  further  discussion  of  the  condition  of  the  Hoosac  and  Grey- 
lock  columns. 


HOOSAO  MOUNTAIN.  105 

Jersey  iron  ores)  10°  to  15°  to  the  north.  It  is  this  pitch  which  enables  us 
to  get  the  series  of  rocks  in  normal  position  and  measure  their  thickness, 
just  on  the  axis  of  the  fold,  for  on  tlie  sides  we  could  never  have  known 
which  rock  was  the  upper  or  the  lower,  owing  to  inversions,  or  whether  the 
apparent  thickness  was  not  produced  by  duplication  of  a  thin  layer  by 
frequent  closed  and  overturned  folds,  as  is  the  case  at  the  southern  end  of 
the  field.  t 

This  anticline  preserves  the  rocks  in  their  normal  position  on  the  east 
side,  but  on  the  west  they  are  folded  under  in  inverse  position,  with  eastern 
dip.  (See  Profile  v",  PI.  vi).  It  is  also  proved  that  at  the  south  end  the 
rocks  have  been  pushed  in  under,  so  that  they  dip  north  instead  of  south,  as 
they  would  naturally  do  if  the  fold  terminated  in  another  dome  at  its  south 
end.  Where  the  normal  east  side  of  the  anticline  and  the  underturned  west 
and  south  sides  meet  we  find  a  great  crumpling,  and  then  the  two  sides 
come  together  and  the  whole  series  strikes  north  to  south.  The  long,  thin 
tongue  of  schist  which  runs  south  from  the  main  mass  is  confoi-mable  to  the 
gneisses  on  both  sides  of  it,  and  must  therefore  lie  in  a  naiTow  trough  in  the 
white  gneisses  which  terminates  at  the  south  end.  The  second  or  west  band 
of  gneisses,  judging  from  its  conformity  to  the  schist  and  from  the  fact  that  it 
runs  into  the  larger  area  of  gneiss  as  one  of  the  series,  after  the  schist  tongue 
ends,  must  be  considered  identical  with  the  gneiss  next  to  the  granitoid 
gneiss,  except  that  in  this  western  band  it  has  more  of  the  quartzite  and 
less  of  the  gneiss  character,  corresponding  to  the  general  change  across 
this  meridian.  This  western  band  would  in  that  case  represent  an  over- 
turned anticline  in  the  white  gneiss,  really  overlain  by  the  limestone, 
which  by  the  overturn  is  made  to  dip  under  it.  This  anticlinal  trough 
of  white  gneiss  pitches  under  the  schist  north  of  the  tunnel.  Lastly,  if 
the  limestone  and  schist  are  the  same  rock  we  must  suppose  that  the 
change  from  one  to  the  other  took  place  in  the  eroded  portion  of  the 
arch  which  connected  the  limestone  with  the  trough  of  schist.  Profile 
v",  PI.  VI,  illustrates  this  theory.  I  am  well  aware  that  such  an  explan- 
ation seems  forced.  It  would  be  much  more  plausible  to  say  that  these 
formations  are  separated  by  north  to  south  faults,  but  all  the  evidence  goes 
against  the  existence  of  faults.     Where  formations  are  found  to  overlie  each 


106         GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

other  conformably  at  so  many  points  and  to  curve  around  in  conformity,  as  at 
the  southwest  comer  of  Hoosac  mountain,  no  kind  of  fault  could  explain 
the  relations.  In  fact,  faults  on  a  large  scale  seem  to  be  absent,  although 
considerable  breaking  may  have  accompanied  the  great  crumpling.  On 
the  summit  of  the  mountain  east  of  Berkshire,  near  the  extreme  southern  end 
of  the  map,  a  small  fault  was  found  between  quartzite  and  schist.  The 
relation  of  the  rocks  at  the  west  end  of  the  tunnel  is  of  much  more  impor- 
tance and  the  explanation  not  easy  without  assuming  a  fault.  It  will  be 
noticed  by  Profile  in,  PI.  v,  that  the  west  edge  of  the  trough  of  schist 
which  runs  along  the  west  slope  of  the  mountain  lies  at  the  tunnel  level,  con- 
siderably west  of  its  position  at  the  surface,  so  that  the  band  of  white  gneiss 
lying  in  the  tunnel  west  of  the  schist  seems  to  lie  on  top  of  it  at  the  surface. 
It  should  be  remembered  that  this  band  of  schist  and  gneiss  west  of  it  have 
been  traced  many  miles  side  by  side  to  the  south  point  of  the  great  fold, 
where  they  curve  together  to  the  east  and  are  found  in  conformable  contact 
and  even  transition  with  each  other.  It  is  therefore  impossible  to  explain 
their  general  relations  by  a  fault,  but  there  may  be  a  fault  separating  them 
for  a  short  distance  here  or  else  an  overturned  fold  in  the  western  gneiss 
curving  far  back  to  the  east,  like  the  great  Grlarus  fold.^  It  would  be  impos- 
sible fully  to  explain  by  words  the  structure  of  the  east  to  west  striking- 
gneisses  just  south  of  the  west  corner  of  the  main  fold.  If  a  piece  of  cloth  is 
worked  into  a  number  of  parallel  folds  or  plaits  and  one-half  of  the  cloth  bent 
around  at  right  angles  to  the  former  general  trend  of  the  plaits,  we  get  just 
the  series  of  transverse  folds  which  exist  on  the  mountain.  The  sections  of 
the  Alps  given  by  Heim  show  folding  of  equal  complication  in  younger 
rocks.  A  model  would  be  the  proper  means  of  representing  this  structure. 
One  result  of  this  work  important  to  future  investigation  in  the  regions 
of  crystalline  rocks  is  that  it  shows  the  possibility,  by  proper  methods  of 
work,  of  determining  much  of  the  stratigraphy  of  these  rocks,  improbable 
as  it  may  seem  at  first  sight.  The  gneisses  of  the  Green  mountains  are 
just  as  susceptible  to  stratigraphic  investigation  as  the  unaltered  sediments 
of  the  Appalachians,  but  the  problem  is  much  more  difficult  owing  to  the 
secondary  structures  produced  by  metamorphism. 

'Heim,  "Mechauismus  der  Gebirgsbildung." 


HOOSAC  MOUNTAIN.  107 

In  the  preceding  pages  of  this  chapter  no  reference  has  been  made  to 
earlier  work  in  this  area,  because  the  httle  recorded  is  hxrgely  based  on  a 
general  survey  of  the  Green  mountains  and  no  attempt  has  been  made  to 
master  the  local  structure  in  detail. 

Most  geological  workers  haVe  given  their  attention  to  the  limestone 
and  schists  west  of  the  axial  range.  Prof.  J.  D.  Dana,  who  has  devoted  so 
many  years  of  his  life  to  the  Taconic  question,  has  published  no  decided 
opinion  on  the  Hoosac  tunnel  series.  The  geological  sections  of  Presi- 
dent Hitchcock  and  Prof.  C.  H.  Hitchcock,^  which  cross  this  area,  are  not 
sufficiently  detailed  for  comparison  in  this  connection. 

Ebenezer  Emmons  alludes  to  Hoosac  mountain  in  his  "Taconic  Sys- 
tem."" He  considers  that  tlie  Hoosac  mountain  schists  were  primary  and 
that  the  lower  Taconic  rocks  (Mount  Grevlock)  were  derived  from  them — a 
theory  by  which  he  explains  the  close  lithological  similarity  which  he  had 
observed  between  the  two  rocks.  It  is  evident  how  inadequate  this  theory 
is  to  explain  this  resemblance  when  we  remember  that  in  the  albite  schist, 
for  instance,  common  to  both  series,  the  albite  crystals  are  metamorphic  in 
both  rocks. 

Emmons  also  describes  (p.  120)  the  contact  of  conglomerate  and  gneiss 
on  Clarksburg  mountain,  north  of  Williamstown. 

President  E.  Hitchcock  ^  regards  as  primary  the  Hoosac  mountain  lime- 
stones at  the  base  and  part  of  the  rocks  further  west.  He  also  speaks  of 
the  transitions  between  quartzite  and  gneiss. 

Prof.  C.  H.  Hitchcock  *  places  a  fault  between  the  limestone  at  the  west 
portal  of  the  tunnel  and  the  Hoosac  mountain  gneiss. 

In  the  writings  of  Prof.  J.  1).  Dana  on  the  Taconic  rocks  there  are  a 
few  allugjons  to  the  Hoosac  mountain  region.  He  speaks  of  the  Stamford 
granite  as  "an  undoubted  Archean  area,"^  but  this  seems  to  be  based  on 
lithological  characters.  He  says,®  "there  is  some  reason  for  making  Hoosac 
mountain  Cambrian." 

'  Geology  of  Massachusetts,  1841.     Geology  of  Vermont,  1861. 

''  Agricultural  Report,  New  York,  p.  R3. 

^  Final  Report,  Geology  of  Massachusetts,  p.  577  et  seq. 

^Geology  of  Vermont,  p.  597. 

s  Amer.  Jour.  Sci.,  vol.  33, 1887,  p.  274. 

6  Ibid.,  p.  410. 


108  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

No  detailed  geological  study  of  the  Hoosac  tuuuel  seems  to  have  been 
published,  which  is  remarkable  considering  the  importance  of  this  engineer- 
ing work  and  the  number  of  experts  who  examined  it  when  in  construction. 

In  the  reports  of  Profs.  James  Hall  and  T.  Sterry  Hunt  as  experts^  the 
general  distribution  of  the  rocks  in  the 'tunnel  is  correctly  given.  Prof 
Hall  noticed  the  transition  from  white  gneiss  to  granitoid  gneiss  at  the  west 
edge  of  the  latter  rock,  and  also  speaks  of  the  micaceous  gneiss  at  the  west 
portal  "resting  against  or  upon  the  limestone,"  an  exposure  no  longer  visible. 

'  Massachusetts  House  Document  No.  9,  January,  1875,  Appendix. 


PLATE  VII. 


109 


PLATE  VI  I. 

A.  Fine  grained  white  gneiss  (Vermont  formation)  from  western  slope  Hoosac  mountain.  From 
a  micropLotograph.     Polarized  light,  x  33. 

In  the  lar"-e  feldspar  twin  u.  the  line  of  twinning  is  oblique  to  the  external  planes  of  the  crystal. 
The  little  black  or  white  round  spots  in  it  are  grains  of  quartz  which  lie  roughly  in  lines  parallel  to 
the  lines  of  arrangoraput  of  the  quartz,  feldspar,  and  mica  outside. 

B.  Gneiss  (Vermont  formation).  Dump  Hoosac  tunnel.  From  a  microphotograph.  Polarized 
light,  X  33. 

A  large  crystal  of  microcliue  (a)  has  been  broken  into  five  parts  in  the  general  crushiug  of  the 
rock,  and  the  groundmass,  composed  of  little  grains  of  quartz  and  feldspar  and  some  mica,  crosses 
it  by  the  cracks. 

110 


J.   S.   OFOLOQICAI 


A.  i'inf  BTaiu 


H«aaav  moimUio.     Fnnu 


ligh., 

A  large  crystal  ••£/(uicroi'line  (a) 
roek,  and  the  givniyftnass,  coaipo'-"'' 
it  by  tlio  fratks 


II);  is  oblii{ac  to  tbo  oxtornal  plai 

i^<vhi.h  ii     roughly  in  iiuu^  iiuijUi:!  lu 
nui'a  <Hit.»»i^ 

cuel.     FronT'lt^icrophotograph.     Polari/,<(l 

tivi!  parts  iu  th^^eueral  i  rushiDK  <>f  the 


U.   S.   GEOLOGICAL  SURVEY 


h-ONOGRAPH    XXIIl       PLATE    VII 


THIN   SECTIONS,   WHITE  GNEISS. 


PLATE  VIII 


111 


PLATE  VIII. 

A.  Fiue  graiueil  white  gueiss  (Vermont  lormation).     Hoosac  uiountaiD.     Microphotograph.    Pol- 
arized light,  X  33. 

Poi-phyritic  feldspar  twin  (a)  containing  Inclusions  of  quartz  and  mica   which  are  arranged 
parallel  to  the  minerals  of  the  groundmass  outside. 

B.  Albite  schist  (Hoosac  schist).     Hoosac  mountain.     Microphotograph.     x  33. 

The  large  crystals  of  albite  (a)  contain  inclusions  of  muscovite,  chlorite,  magnetite,  and  quartz. 
The  gentle  curving  of  the  mica  of  the  groundmass  between  these  feldspars  is  well  shown. 

112 


U,   B.   QEOLOQICAL  SUHVEV 


MONOORAPH    XX<II      PU^TE   VIII 


'  THIN  SECTIONS.   " 


\.  Fine  graiufd  wUit*  j^tu-ino  i  v 
iiri7.t'<l  light,  X  '■'3. 

I'orphyritio  t'«lilsi)ar  twin  (a)  containinfr  inclusions  of  quart)',  ami   iiiioa   which  are  arranged 
)>art<  ■.I'." 

^  ■  ■  ^  13. 

I  ^<r  ^r\)'  '■      'I'Njf' ■ '""ifiiefit^,  ami  quartz. 

'I'll"  ^  jT       \  ui  -  •yi  •  i-w      rki3|i.imii^wcll  abown. 

llii 


U.   S.   GEOLOGICAL  SURVEY 


MONOGRAPH    XXIIl       PLATE    VIII 


THIN  SECTIONS,  WHITE  GNEISS  AND  ALBITE-SCHIST._ 


PLATE  IX. 


MON  XXIII 8  '  ii>^ 


PLATE  IX. 

A.  "Amphibolite."    Diorite  dike.     Hoosac  moiiutain,  south  of  Cheshire.     Microphotograph,  x  33. 
Crystalloids  or  grains  of  plagioclase  feldspar  (a)  and  of  brown  hurnblende  (fc)  are  seen  around 

the  edge  of  the  figure.  In  the  center  we  have  an  aggregate  of  irregular  patches  of  secondary  feld- 
spar, green  hornblende,  epidote,  etc.,  forming  a  confused  aggregate,  little  veins  of  which  are  seen  to 
penetrate  the  feldspars  or  pass  between  them. 

B.  Amphibolite.     Mount  Holly,  Vermont.     Microphotograph;  polarized  light  x  33. 

The  large  black  areas  are  a  deep  greenish-brown  hornblende,  surrounded  by  a  fringe  of  light 
green  hornblende.  This  shows  best  in  the  crystal  in  the  center  («)  with  the  fringe  (b).  The  portion 
between  the  black  crystals  is  an  aggregate  of  epidote  prisms,  masses  of  green  hornblende,  and 
feldspar. 

114 


M  ■'NO.j'^APH 


THIM  SECTIONS,  DIORITE  AND  AlllWl»BOL(TE. 


A.  "Amphibolite.'      I 
Crystalloids  or  graiiiM  n 

the  eUg«<  of  the  ';.'"■■       <•    > 
spar,  green  boi ; 
penetr.'ite  <'■ 

B.  A" 
T'  lack 

pretM  iile.     This  shd 

botwcoi.   Uiu  l)lack  cryst 
)'<-l<l«j'ar. 


■oil)  ,  Veri: 

i\  lib  ;ir>'  ;i   il 


Mi'To|ihotograph,  X  33. 
■  ndc  (fc)  are  secu  around 
..     |i:itch<4  of  secondary  t'vhl- 
tle  veiiie  of  >vlii(h  are  iu<en  lu 


)hol< igi  .ipti ;  polari/ed  Uttht  X  'X'- 

le,  siirroiiDdod  by  a  frmgi-  of  light 

ith  tlic  friiij.r  (I)).     The  portion 

epidutc  jiriouiE,   iiiasftiw  of  green  huniblolidu,  and 


U.   S.   GEOLOGICAL  SURVEY 


MONOGRAPH    XXIII       PLATE    IX 


THIN  SECTIONS,   DIORITE  AND  AMPHIBOLITE. 


PLATE  X. 


115 


PLATE  X. 

A.  Qiiartzite-congloiiierate  (Vermont  form.ation).  Stone  hill,  Williamstown,  Mass.  Microphoto- 
graph;  polarized  ligbt,  x  27. 

The  shadowy  area  filling  the  left  half  is  one  of  the  masses  of  crushed  blue  (juartz  which  shows  the 
so-called  "wavy"  extinction  in  polarized  light.  At  the  top  it  is  seen  passing  into  the  quartz  mosaic  of 
the  "gronndmass."  At  the  bottom  and  lower  right  side  a  crystal  of  microcline  has  been  faulted 
several  times  and  the  fine  quartz  of  the  groundmass  penetrates  it. 

B.  Crumpled  metamorphic  conglomerate  (Vermont  formation).  Hoosac  mountain,  bluffs  south  of 
Spruce  hill,  near  that  of  Fig.  17.     About  one-eighteenth  natural  size. 

These  pebbles  are  grannlitic  and  by  pressure  have  been  gently  crumpled.  This  figure  represents 
the  transitional  form  between  the  conglomerate  and  tlie  white  gneiss;  in  the  latter  the  grannlitic 
lenses  remind  us  of  pebbles,  but  they  have  lost  their  shape. 

116 


U.    S.    GEOLOGICAL  SURVEY 


MONOGRAPH    XXIII       PLATE   X 


QUARTZITE   CONGLOMERATE   AND  CRUMPLED   METAMORPHIC  CONGLOMERATE. 


PLATE  XI. 


117 


PLATE  XI. 

A.  Looking  north  over  the  crest  of  Hoosac  mountain  from  the  northern  end  of  the  granitoid 
gneiss  (compare  PI.  v.,  Profile  ix),  showing  the  outcropping  edges  of  the  northerly  dipping  (pitch- 
ing) beds  of  conglomerate  gneiss  and  albite  schist.     From  a  drawing  by  Josiah  Pierce,  jr. 

B.  Profile  of  Hoosac  mountain  from  Spruce  hill  southward,  looking  west. 

This  includes  the  contact  of  all  three  formations — granitoid  gneiss  (Stamford  gneiss),  conglomerate 
(Vermont  gneiss),  and  albite  schist  (Hoosac  schist).  The  northerly  pitch  of  the  axis  and  consequent 
overlay  of  the  formations  to  the  north  shows  plainly  in  the  long  gentle  northward  slope  and  sharp 
bluffs  to  the  south.  The  rounded  granite  topography  of  the  coarse  gneiss  is  also  in  marked  contrast 
with  the  serrations  produced  by  conglomerate  and  schist.     Cf.  Plate  v,  Profiles  ix  and  x. 

118 


EREATUM. 
Plate  XI.— Legends  to  Figs.  A  and  B  sliould  be  transposed. 


U,   S.   GEOLOGICAL  SURVEY 


MONOGRAPH    XXHI      PLATE    3 


5^-  "i    ^^    li^rii 


;%. 


I ,-  «si^>^-5H 


-■:*.«5rwt.-"-'' 


"•^^i 


A.    VIEW  NORTH  OVER   CREST  OF  HOOS«C  MOUNTAIN. 


jl^/^-  ^'^^Jf  ll^^v^fe- 


B.    PROFILE  OF  HOOSAC  MOUNTAIN    FBOM  SPRUCE    HILL  SOUTHWARD,    LOOKING  WEST. 


P^RT     III. 


MOUNT  GREYLOCK: 

ITS  AREAL   AND  STRUCTURAL  GEOLOGY 


By  T.  n'ei.so:n  d^le. 


119 


CONTENTS. 


Page. 

Outline  of  tliis  paper 125 

Historic 131 

Physiographic 133 

Structural 136 

Types  of  structure 138 

Correlation  of  cleavage  aud  stratification 155 

Pitch 157 

Structural  priuciples 157 

Structural  transverse  section? 158 

Transverse  section  G 160 

Transverse  sections  H,  I 166 

Transverse  sections  A-F,  J  -0 169 

General  jjitch  of  the  folds 175 

Longitudinal  sections 175 

Longitudinal  section  P 175 

Longitudinal  section  Q 176 

Longitudinal  sections  R' .  R" 177 

RpsumtS,  structural 177 

Lithologic  strat'graphy 179 

Vermont  formation 179 

Stockbridge  limestone 179 

Berkshire  schist 180 

Bello wsiiipe  limestone 180 

Grey  lock  schist 180 

Petrography 181 

The  Vermont  formation 181 

The  Stockbridge  limestone 181 

The  Berkshire  schist 182 

The  Bellowspipe  limestone 184 

The  Greylock  schist 186 

Thickness 188 

Geologic  age 189 

R<!sum6,  lithologic  stratigraphy 190 

Areal  and  structural 191 

Relations  of  geology  to  topography 192 

Appendix  A :  Stone  hill  near  Williamstown 197 

Appendix  B :  New  Ashford 202 

121 


ILLUSTRATIONS. 


o 


Page. 

Pl.  XII.  Mount  Greylock,  eastern  side 130 

XIII.  Mount  Greylock,  western  side 132 

XIV.  Southern  summit  of  Mount  Greylock 134 

XV.  Southern  side  of  Mount  Greylock 136 

XVI.  Southern  end  of  Ragged  mountain 160 

XVII.  The  north-south  part  of  Hopper 192 

XVIII.  Greylock  sections  A,  B,  C,  D 

XIX.  Greylock  sections  E,  F 

XX.  Greylock  sections  G,  H,  I 

XXI.  Greylock  sections  J,  K,  L,  M 

XXII.  Greylock  sections  N,  O -• 

XXIII.  Greylock  longitudinal  sections  P,  Q,  R 

Fig.   30.  Mount  Greylock,  north-northwestern  side 136 

31.  Albitic  sericite-schist  in  contact  with  limestone 138 

32.  Sericite-schist  with  two  foliations,  in  contact  with  limestone 139 

33.  Sericite-schist;  specimen  with  two  foliations 139 

34.  Thin  section  illustrating  origin  of  cleavage 140 

35.  Sketch  of  ledge  south  of  Sugarloaf ;  cleavage  in  both  limestone  and  schist 140 

36.  Limestone  block  with  cleavage,  Sugarloaf 141 

37.  Limestone  ledge  with  Cleavage,  east  of  Sugarloaf 141 

38.  Weathered  limestone  from  East  mountain 142 

39.  Polished  surface  of  limestone  shown  in  Fig.  38 142 

40.  Weathered  limestone  with  mica  in  cleavage  planes 143 

41.  Specimen  of  sericite-schist  showing  stratifioatiou  and  cleavage.  Bald  mountain 144 

42.  Specimen  of  sericite-schist  showing  only  cleavage,  Symouds  peak 144 

43.  Section  of  specimen  shown  in  Fig.  42 145 

44.  Section  of  specimen  of  sericite  schist,  top  of  Mount  Greylock 145 

15.  Microscope  drawing  of  sericite  schist,  top  of  East  mountain *- 146 

46.  Specimen  of  sericite  schist  one-fourth  mile  south  of  Mount  Greylock 147 

47.  Diagrams  showing  relation  of  quartz  laminse  to  cleavage 148 

48.  Lodge  of  sericite-schist,  junction  of  Gulf  and  Ashford  brooks 148 

49.  Part  of  ledge  shown  in  Fig.  48 149 

50.  Section  of  sericite-schist  with  quartz  lamina,  from  Bald  mountain 150 

51.  Ledge  of  mica-schist  in  Readsboro,  Vermont,  with  quartz  in  both  foliations 151 

52.  Sericite-schist  with  two  cleavages,  Goodell  hollow 152 

123 


124  tLLtfSTRATIOKS. 

Page. 

Fig.  53.  Section  of  sericite-schist,  one-fourth  mile  soutli  of  Greylock  top 153 

54.  Sericite-schist,  one-fourth  mile  southwest  of  Greylock  top 154 

55.  Diagram  showing  fault  between  schist  and  limestone 154 

56.  Section  of  sericite-schist,  Bald  mountain  spur 155 

57.  Diagrams  showing  relation  of  slip  cleavage  to  stratification,  clips  opposite 156 

58.  Quartz  lamina'  in  schist,  west  side  of  Deer  hill 156 

59.  Diagrams  showing  relation  of  slip  cleavage  to  stratification,  both  dips  east  or  west 157 

60.  Minor  pitching  limestone  folds 157 

61.  Cross-section  G 160 

62.  Section  of  syncline  at  south  end  of  Ragged  mountain 161 

63.  Cross-section  H 166 

64.  Cross-section  1 166 

65.  Cross-sections  A,  B 169 

66.  Cross-section  F 171 

67.  Cross-sections  J,  K,  L 172 

68.  Structure  of  schist  on  south  side  of  Saddle  Ball 173 

69.  Cross-sections  M,  N,  O - 173 

70.  Structure  iu  schist  west  of  Cheshire  reservoir 174 

71.  Longitudinal  sections  P,  Q,  R 175 

72.  Continuity  of  the  folds  on  the  Greylock  sections 178 

73:  Albitic  sericite-schist,  typical  Greylock  schist 188 

74.  Outline  sketch  of  Round  rocks 194 

75.  Sketch  of  Greylock  mass  from  the  southwest 195 

76.  Cross-sections  S,  T,  U,  Stone  hill 198 

77.  Sketch  of  protruding  limestone  anticline 202 

78.  Diagram  map  of  Quarry  hill.  New  Ashford ~- 202 

79.  Cross-section  of  Quarry  hill,  New  Ashford 203 


OUTLINE  OF  THIS  PAPER. 


Mount  Gi'6ylock,  or  Saddle  mouiitain,  in  northwestern  Massachusetts,  has  been 
studied  off  and  on  by  geologists  for  seventy  years.  The  literature  is  given  on  p.  131. 
The  general  synclinal  structure  of  the  mountain  is  well  known.  This  description  is 
based  upon  the  new  topographic  map  of  the  U.  S.  Geological  Survey,  and  upon 
the  results  of  recent  orographic  science.  Mr.  J.  Eliot  Wolff  has  done  the  petrographic 
work. 

The  mountain  consists  mainly  of  one  central  and  two  lateral  subordinate  ridges, 
all  trending  about  north-northeast  to  south-southwest.  With  its  spurs  it  forms  a 
topographic  unit  and  measures  16^  miles  in  length  and  averages  about  3^  in  width. 
Its  aspects  from  the  north,  south,  east,  and  west  are  described  on  p.  134  (Pis.  xii, 
xiii-xv).  Tlie  "saddle"  is  formed  by  a  depression  in  the  south wiBsterly  bend  of  the 
central  ridge,  between  Greylock  summit  (3,505  feet)  on  the  north  and  Saddle  Ball 
(3,300  feet)  on  the  south.  These  are  about  2  miles  apart,  and  the  lowest  part  of  the 
saddle  is  605  feet  lower  than  Greylock  summit. 

Structural. — Tlie  rocks  are  all  metamori^hic  and  of  few  kinds,  crystalline  lime- 
stone, quartzite,  and  schists.  The  key  to  the  structure  is  in  the  distinction  between 
cleavage  foliation  and  stratification  foliation.  The  principal  recent  and  oldei-  liter- 
atui-e  of  that  subject  is  given  on  p.  137.  Thepiienomena  of  cleavage  and  stratifica- 
tion and  pitch,  as  they  occur  on  Greylock,  are  illustrated  by  ten  typical  cases.  These 
lead  to  the  adoption  of  the  following  structural  principles:  I.  Lamination  in  the 
schist  or  the  limestone  may  be  either  stratification  foliation  or  cleavage  foliation  or 
both,  or  sometimes,  in  limestone  at  least,  "  false  bedding."  To  establish  conformability, 
the  conformability  of  the  stratification  foliation  must  be  shown.  II.  Stratification 
foliation  is  indicated  by:  (a)  the  course  of  minute  but  visible  plications ;  (b)  the  course 
of  the  microscopic  iilications;  (c)  the  general  course  of  the  quartz  laminiB  whenever 
they  can  be  clearly  distinguished  from  those  which  lie  in  the  cleavage  planes.  III. 
Cleavage  foliation  may  consist  of:  («)  planes  produced  by  or  coincident  with  the 
faulted  limbs  of  the  minute  plications;  (b)  planes  of  fracture,  resembling  joints  on  a 
very  minute  scale,  with  or  without  faulting  of  tlie  plications;  (c)  a  cleavage  approach- 
ing slaty  cleavage,  in  which  the  axes  of  all  the  particles  have  assumed  either  the 
direction  of  the  cleavage  or  one  forming  a  very  acute  angle  to  it,  and  where  stratified' 

125 


126         GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

tioii  foliation  is  no  longer  visible.  lY.  A  secondary  cleavage,  resembling  a  minute 
jointing,  occurs  in  scattered  localities.  V.  The  degree  and  direction  of  the  pitch  of  a 
fold  are  often  indicated  by  those  of  the  axes  of  the  minor  plications  on  its  sides.  VI. 
The  strikes  of  the  stiatiflcation  foliation  and  cleavage  foliation  often  differ  in  the  same 
rock,  and  are  then  regarded  as  indicating  a  pitching  fold.  VII.  Such  a  correspondence 
exists  between  the  stratification  and  cleavage  foliations  of  the  great  folds  and  those 
of  the  minute  plications  that  a  very  small  specimen  properly  oriented  gives,  in  many 
cases,  the  key  to  the  structure  over  a  large  portion  of  the  side  of  a  fold. 

On  these  principles  twelve  com^ilete  and  three  partial  transverse  sections  have 
been  constructed  across  the  Greylock  mass  (Pis.  xviii-xxii).  These  show  that  the 
range  consists  of  a  series  of  more  or  less  open  or  compressed  synclines  and  anticlines, 
which,  beginning  near  North  Adams,  increase  southerly  in  number  and  altitude  with 
the  increasing  width  and  altitude  of  the  schist  area,  and  then,  from  a  point  about  a 
mile  and  a  half  south  of  the  summit,  begin  to  widen  out,  and  to  diminish  in  number 
and  height  until  they  finally  pass  into  a  few  broad  and  low  undulations  west  of 
Cheshire.  Between  that  point  and  the  villages  of  Berkshire  and  Lanesboro  the  folds 
become  sharper  and  more  compressed,  and  the  schist  area  rapidly  narrows,  termi- 
nating within  a  short  distance  of  Pittsfield.  The  two  most  comprehensive  and  best 
substantiated  of  these  sections  (G  and  I)  begin  near  South  Adams,  cross  the  central 
ridge  north  and  south  of  the  summit,  then  follow  the  two  great  western  spurs,  and 
end  near  South  Williamstown.  The  sections  are  described  on  p.  160,  the  first  two  in 
some  detail.  The  section  lines  on  the  map  (PI.  i)  and  the  epitomized  sections  in  Fig. 
72  on  p.  178  show  the  relations  of  the  fifteen  sections  to  each  other. 

Resume,  structural. — Mount  Greylock  with  its  subordinate  ridges  is  a  synclinorium 
consisting  in  its  broadest  portion  of  ten  or  eleven  synclines  alternating  with  as  many 
anticlines.  While  the  number  of  these  minor  synclines  is  so  considerable  at  the  sur- 
face, in  carrying  the  sections  dowuwai'd  they  resolve  themselves  chiefly  into  two 
great  synclines  with  several  lateral  and  minor  ones.  The  larger  of  these  two  forms 
the  central  ridge  of  the  mass ;  the  smaller  one,  east  of  it,  forms  Eagged  mountain  and 
an  inner  line  of  foot-hills  farther  south.  The  anticline  between  these  coincides  with 
the  Bellowspipe  notch;  that  on  the  west  of  the  central  syncline  is  on  the  west  side 
of  the  north-south  part  of  the  Hopper.  The  major  and  central  syncline  is  so  com- 
pressed east  of  Symonds  peak  (Mount  Prospect)  and  Bald  mountain,  and  its  axial 
plane  is  so  inclined  to  the  east  that  the  calcareous  strata  which  underlie  the  central 
ridge  have  on  its  west  side  a  westerly  dip.  Farther  south  this  syncline  opens  out, 
and  all  the  relations  become  more  normal.  On  either  side  of  those  two  main  synclines 
the  sub(  irdinaitc  folds  are  more  or  less  open  and  have  their  axial  planes  vertical  or  inclined 
east  or  west.  The  long  undulations  in  the  axes  of  these  synclines  are  shown  in  four 
longitudinal  sections  (PI.  xxiii):  Section  P,  the  eastern  or  Ragged  mountain  syncline; 
Q,  the  central  or  Greylock  syncline,  and  E'  R",  portions  of  two  of  the  minor  synclines 
on  the  west  flank  of  the  mass.     In  each  of  the  sections  P  and  Q  the  trough  bottom 


MOUNT  GREYLOCK.  127 

deepens  at  two  points.  In  the  eastern  syncliue,  P,  the  deeper  part  of  the  northern 
depression  is  shown  to  be  about  under  the  center  of  Ragged  mountain,  while  in  the 
central  one,  Q,  the  deeper  part  of  the  northern  depression  seems  to  be  about  2  miles 
farther  south,  between  Greylock  and  Saddle  Ball  and  near  Greylock  summit.  The 
northern  side  or  edge  of  this  great  double  trough  is  at  the  extreme  north  end  of  the  Grey- 
lock mass ;  section  Q  begins  at  Clarksburg  mountain,  and  its  southern  edge  is  between 
7J  and  8J  miles  distant,  near  Round  Rocks  and  on  the  southeast  spur  of  Saddle  Ball. 
South  of  these  main  troughs  is  another  pair,  the  centers  of  which  lie  west  of  Cheshire 
reservoir.  To  the  west  of  these  two  long  axes  the  mountain  mass  is  made  up  of 
numerous  minor  folds,  which  do  not  show  the  continuity  seen  in  P  and  Q.  It  will  be 
seen  that  the  direction  of  these  two  main  synclines  represented  by  P  and  Q  is  north- 
northeast  by  south-southwest,  thus  nearly  parallel  with  the  direction  of  the  valley 
lying  between  the  Clarksburg  granitoid  gneiss  mass  and  Hoosac  mountain,  and  that 
at  the  south  end  they  converge  and  perhaps  unite  in  tke  narrow  schist  ridge 
between  Berkshire  and  Lanesboro  villages.  Traversing  the  folds  of  this  canoe-like 
complex  synclinorium  is  a  cleavage  foliation,  sometimes  microscopically  minute,  dipping 
almost  uniformly  east.  This  cleavage  foliation  is  distinct  from  the  "slaty  cleavage," 
early  described  by  Sedgwick,  Sharpe,  and  Sorby  and  reproduced  experimentally  by 
Tyndall  and  Jaunettaz,  and  consists  sometimes  of  a  minute,  abrupt,  joint-like  fractur- 
ing of  the  stratification  laminsB,  but  more  usually  of  a  faulting  of  these  laminae  as  the 
result  of  their  extreme  plication — a  mode  of  cleavage  ("Ausweichungsclivage")  so 
well  described  by  Heim  and  recently  reproduced  in  part  by  Cadell  by  a  slight 
modification  of  the  experiments  made  by  Prof.  Ali^house  Favre,  of  Geneva,  in  1878. 
(See  foot-notes,  p.  137.)  This  slip  cleavage,  when  carried  to  its  extreme,  results  in  a 
form  of  cleavage  very  much  approaching,  although  not  identical  with,  slaty  cleavage. 
To  the  unaided  eye  all  traces  of  stratification  are  lost,  and  even  under  the  microscope 
they  are  so  nearly  lost  as  to  be  of  no  avail  in  determining  the  dip.  This  and  the 
regular  slip  cleavage  often  occur  in  close  proximity. 

Lithologic  stratigrapliy. — There  are  five  more  or  less  distinct  horizons  in  the  Grey- 
lock mass.  The  following  descriptions  are  based  upon  Mr.  WolfFs  petrographic  deter- 
minations, beginning  above: 

The  Greylock  schist  (Sg).  Muscovite  (sericite),  chlorite,  and  quartz  schist,  with  or 
without  biotite,  albite,  magnetite,  tabular  crystals  of  interleaved  ilmenite  and  chlorite, 
ottrelite,  microscopic  rutile,  and  tourmaline.  Thickness,  1,500  to  2,200  feet.  Part  of 
Emmons's  pre-Cambrian  or  Lower  Taconic  No.  3  ("talcose  slate"),  Walcott's  Hudson 
River  (Lower  Silurian). 

BeUoicspipe  limestone  (Sbp).  Limestone  more  or  less  crystalline,  generally  mica- 
ceous or  pyritiferous,  passing  into  a  calcareous  schist  or  a  feklspathic  quartzite,  or  a 
fine-grained  gneiss  with  zircon  and  microcline,  in  places  a  noncalcareous  schist.  The 
more  common  minerals  are  graphite,  pyrite,  albite,  microscopic  rutile,  and  tourma- 
line; rarely,  galena  and  zinc  blende.    Thickness,  600  to  700  feet.    Par£  of  Emmons's 


128  GltEEN  MOUNTAINS  IN  MASSACHUSETTS. 

pre-Cambi'ian  or  Lower  Taconic  No.  3  ("talcose  slate"),  Walcott's  Hudson  Eiver  (Lower 
Silurian). 

The  Berkshire  schist  (Sb).  Schist  like  the  Greylock  schist,  but  more  frequently  cal- 
careous and  i)lumbaginoiis,  especially  toward  the  underlying  limestone  (€Ss) ;  thick- 
ness, 1,000  to  2,000  feet.  Part  of  Emmons's  pre-Cambrian  or  Lower  Taconic  No.  3 
("  talcose  slate"),  Walcott's  Hudson  Eiver  (Lower  Silurian). 

The  tStocTchridge  limestone  (■£?&).  Limestone,  crystalline,  in  places  a  dolomite, 
quartzose  or  micaceous,  more  rarely  feldspathic,  very  rarely  fossiliferous.  Galena 
and  zinc  blende  rare.  Irregular  masses  of  iron  ore  (limonite)  associated  sometimes 
with  manganese  ore  (pyrolusite).  Thickness  1,200  to  1,400  feet.  Emmons's  pre-Cam- 
brian or  Lower  Taconic  No.  2  ("Stockbridge  limestone"),  Walcott's  Hudson  River 
(Lower  Silurian). 

The  Vermont  formation  {-Cv).  Quartzite,  cropping  out  in  the  Greylock  area  only 
once,  but  probably  underlying  the  entire  mass.  Thickness,  800  to  900  feet,  Emmons's 
pre-Cambrian  or  Lower  Taconic  No.  1  ("granular  quartz"),  Walcott's  "O/ewei^ws" 
(Lower  Cambrian).    Total  thickness  of  the  series,  5,000  to  7,200  feet. 

The  estimates  of  thickness  are  based  upon  the  sections.  The  difference  in  the 
estimates  arises  partly  from  the  varying  amount  of  thickening  in  plication.  The 
actual  thickness  is  probably  less  than  the  minimum  figures  given  above,  and  possibly 
much  less.  The  maximum  thickness  of  the  entire  series  does  not  exceed  the  minimum 
thickness  attributed  to  the  Lower  Silurian  in  the  Appalachian  region.  See  page  190 
for  a  tabular  arrangement  of  these  results. 

Areal  rjeology. — The  accompanying  geographic  map  of  Greylock  and  the  adja- 
cent masses  presents  a  great  body  of  the  Berkshire  schist  almost  surrounded  by 
the  underlying  Stockbridge  Umestone.  The  Berkshire  schist  sends  out  tongues,  cor- 
responding to  synclines,  into  the  Stockbridge  limestone  area.  There  are  also  reenter- 
ing angles  of  limestone  in  the  schist  area,  corresponding  to  anticlines.  There  are 
isolated  schist  areas  which  are  more  or  leas  open  synclines,  and  isolated  limestone 
areas  which  are  compressed  anticlines  protruding  through  the  overlying  schist, 
exposed  by  erosion.  These  relations  recur  between  the  Bellowspipe  limestone  (Sbp) 
and  the  Greylock  phyllite  (Sg),  but  the  limestone  area  southwest  of  Cheshire  appeara 
to  be  a  syncline. 

Relation  of  geology  to  to})ography. — The  physically  and  chemically  more  resistant 
schists  form  the  more  elevated  portions  and  the  steeper  slopes,  while  the  broad  valleys 
and  gentler  undulations  about  the  mountain  generally  correspond  to  limestone  areas. 
The  limestone  and  calcareous  schist  of  the  Bellowspipe  limestone  horizon  consti- 
tute the  benches  of  agricultural  land  high  up  on  the  sides  of  the  mountain  and  the 
Notch  ;  and  to  the  presence  of  this  rock  also,  together  with  a  northerly  pitch,  is  due 
the  deep  incision  in  the  central  crest  between  Saddle  Ball  and  Round  rock.  (See  sec- 
tion Q  and  PI.  xiii  and  Fig.  74.  The  north  to  south  part  of  the  Hopper  (PI.  xvii) 
is  due  to  the  trend  and  upturned  edges  of  the  calcareous  belt,  and  possibly  also  to 


MOUNT  GKEYLOCK.  129 

the  minor  anticline  on  the  west  side  of  this  part  of  the  Hopper.  The  deep  east  to 
west  incisions  on  both  sides  of  the  mountain  are  the  results  of  erosion  crossing  the 
strike,  while  the  great  spurs  on  the  west  side  are  portions  of  the  original  mass  left 
by  this  erosion.  The  saddle  between  Greylock  summit  and  Saddle  Ball  seen  from 
the  south  (PI.  XV)  is  due  to  the  central  syucline  of  the  mass  (Sections  I  and  K). 
The  broader  saddle  seen  from  Mount  Equinox  on  the  north-northwest  (Fig.  30, 
p.  130)  is  due  to  the  great  trough  in  the  central  syncline  (Section  Q).  The  center  of  this 
trough  is  the  deepest  part  of  the  entire  syuclinorium. 

In  Appendix  A,  Stone  hill,  near  Williamstown,  and  in  Appendix  B,  New  Ashford, 
are  described  in  some  detail.  The  former  is  accompanied  by  three  transverse  sec- 
tions, S,  T,  U,  which  are  crossed  by  the  longitudinal  section  R',  from  which  it  appears 
that  a  subordinate  syncline  passes  through  Stone  hill  and  Deer  hill,  whence  it  prob- 
ably continues  southward  through  East  and  Potter  mountains.  The  relation  between 
Stone  and  Deer  hills  is  analogous  to  that  between  Clarksburg  mountain  and  Grey- 
lock. 

MON  XXIII y 


I.   GEOLOOICAL  SURVEt 


Chc^w'0^ 


V/uGz/ioa 


,S-^lUCU/iX 


uV/iiC^j^ZaoIits 


'JUfu^jxeJi'lt. 


^.Atican^ 


From  a  point  on  Hoomc  mountain  about  4  inile*  soulh  of  NortK  Atlamt  anil  500  feet  shove  Hooiic  nvei,  showing  Ihv  nia»  from  North  Adams  10  Chethiie,  1  1 


MOUNT  GHEYLOCK    EASTERN  SIDE. 

iiles.      In  Ihu  northern  half,  the  high  bench  of  arable  la..d  (marked  by  2  b.ids»,  Bellowspipe  limeslone,  sepatated  ('omtho  Hooiic  valley  by  a  steep  of«a  of  the  Berkshire  schis! 
foothills  of  Berkshire  schist  separated  from  the  central  mass  by  areas  of  Bellowspipe  limestone      F'"m  Photographs 


1  bench  the  Ragged  mountain  mass,  Greyloek  schist,  separated  from  the  central  ridge  by  the  Notch;  m  the  southerr.  half  the 


MOUNT  GREYLOCK:  ITS  STRUCTURAL  AND  AREAL  GEOLOGY.' 


By  T.  Nelson  Dale. 


HISTORIC. 


Mount  Greylock,  or  Saddle  inountaiii,  has  been  an  object  of  interest  to 
geologists  for  seventy  years.  The  most  important  work  in  structural  and 
areal  geology  that  has  been  done  on  the  mountain  is  that  of  Prof  Chester 
Dewey  (1817-1829),  Prof  Ebenezer  Emmons  (1833-1855),  Prof  Edward 
Hitchcock  (1856-1861),  and  Prof  James  D.  Dana  (1871-1887.)  Prof  Em- 
mons built  upon  and  extended  the  investigations  male  by  Prof  Dewey. 
In  the  writings  of  Profs.  Dewey,  Emmons,  Hitchcock,  and  Dana,"  the 
general  boundaries  between  the  limestone  of  the  Hoosic  and  Green  river 
valleys,  and  the  schists  of  Greylock  and  Deer  hill,  and  the  qiiartzite  of 
Stone  hill  are  given.     The  synclinal  structure  of  the  Greylock  mass,  and 

'  A  report  to  Prof.  Raphael  Pumpilly,  in  charge  of  tlio  Archean  Division,  covering  field  work  dune 
nndcr  his  direction  in  the  sninmers  of  1886,  1887.  and  part  of  1888,  by  the  writer,  with  the  assistance 
duriua-  1886  and  part  of  1887  of  Mr.  Wm.  H.  Hobbs. 

-  Amos  Eaton  :     Index  to  the  Geology  of  the  Northern  States.     1818.     2d  ed.  1820. 

Chester  Dewey :  Sketch  of  the  mineralogy  and  gtology  of  the  vicinity  of  Williams  College, 
Willianistown,  Massachusetts  (in  a  letter  to  the  editor  of  tlni  American  .Journal  of  Science,  dated 
January  27,  1819,  witli  a  geologic  map  and  .section  of  the  northwest  part  of  Massachusetts).  Am. 
Jour.  Sci.,  ser.  i,  vol.  1,  1819,  p.  337. 

Chester  Dewey :  Geological  section  from  the  Taconick  range  in  Williamstowu  to  the  city  of 
Troy  on  the  Hudson.     Am.  Jour.  Sci.,  ser.  i,  vol.2,  1820,  p.  24fi. 

Amos  Eaton:  Geological  and  agricultural  survey  of  the  district  adjoining  the  Erie  canal. 
1824.  (This  includes  a  section  from  Hoosac  mountain,  Savoy,  to  the  Hudson  at  Troy.  It  is  repro- 
duced in  a  paper  by  C.  D.  Walcott  in  the  Tenth  Annual  Kept.,  U.  S.  Geol.  Survey,  1888-89,  p.  525.) 

Chester  Dewey :  A  sketch  of  the  geology  and  mineralogy  of  the  western  jiart  of  Massachusetts  and 
a  small  part  of  the  adjoining  states  (with  a  geologic  map  of  tlie  county  of  Herkshire,  Massachusetts, 
and  of  a  small  part  of  the  adjoining  states).     Am.  .lour.  Sci.,  ser.  I,  vol.  8,  ])art  2,  1824,  ]).  1. 

Amos  Eaton:  A  geological  nomenclature  for  North  America,  founded  uimn  surveys  taken  under 
the  direction  of  the  Hon.  Stephen  Van  Kens.selaer.     Albany,  1828. 

Chester  Dewey :     A  general  view  of  Berkshire  county,  forming  pai  1 1  of  "  A  history  of  the  county  of 

131 


132  GKEEN  MOUNTAINS  IN  MASSACHUSETTS. 

the  relation  of  the  Hmestoiie  to  the  schist  were  pointed  out  by  Profs.  Hall 
and  Emmons,  and  confirmed  by  Profs.  Hitchcock  and  Dana,  and  the  com- 
plex character  of  that  syncliue  was  recently  conjectured  by  Prof.  Dana. 
Moreover,  scattered  through  the  writings  referred  to,  are  a  number  of 
important  observations  on  portions  of  the  mountain,  to  which  reference  will 
be  made  in  proper  place. 

Of  these  writings,  those  of  Profs.  Emmons  and  Dana  include  the 
Taconic  question,  into  the  consideration  of  which  the  structural  and  areal 
geology  of  the  Greylock  mass  partly  enters.  Notwithstanding  the  time 
that  has  elapsed  since  a  geologic  hammer  was  first  applied  to  Mount  Grey- 
lock,  and  notwithstanding  the  number  and  ability  of  the  geologists  who 
have  lived  and  worked  in  its  vicinity,  little  has  been  accomplished  beyond 

Herkshire,  Massachusetts,  by  gentlemen  iu  tho  county,  clerijymcn,  and  Laymen."  Pittsfield,  1829  (p. 
190,  "Geology,"  and  "a  geological  map  of  the  county  of  BerksUiro,  Massachusetts,  audof  asmall  part 
of  the  adjoining  states,  1824"). 

Edward  Hitchcock :  Report  on  the  geology,  mineralogy,  botany,  and  zoology  of  Massachusetts. 
First  and  second  editions,  Amherst,  1835. 

Edward  Hitchcock :  Final  report  on  the  geology  of  Massachusetts.  Amherst  and  Northampton, 
1841. 

Ebeuezer  Emmons :  Taconic  system,  forming  chap,  vii  of  the  Geology  of  Now  York,  part  u.  Nat. 
Hist,  of  N.  Y.,  part  iv,  Albany,  1842. 

Ebenezer  Emmons :  The  Taconic  system,  based  on  observations  in  New  York,  Massachusetts, 
Maine,  Vermont,  and  Rhode  Island,  Albany,  1844. 

Ebenezer  Emmons:  The  Taconic  system,  forming  chap.  v.  of  vol.  1,  of  the  Agriculture  of  New 
York.     Nat.  Hist,  of  N.  Y.,  part  v,  Albany,  1846. 

Ebenezer  Emmons :    American  Geology,  vol.  1,  part  ii,  Albany,  1855. 

Edward  Hitchcock :  Report  on  the  Geology  of  Vermont :  descriptive,  theoretical,  economical,  and 
scenographical.     Proctorsville,  Vermont,  1861,  vol.  1,  p.  255,  vol.  2,  p.  595,  pi.  XV,  fig.  5. 

James  D.  Dana :  On  the  quartzite,  limestone,  and  associated  rocks  of  the  vicinity  of  Great  Bar- 
rington,  Berkshire  county,  Massachusetts.     Am.  .Jour.  Sci.,  ser.iil,  vol.  6,  1873,  p.  273. 

James  D.  Dana:  An  account  of  the  discoveries  iu  Vermont  Geology  of  the  Rev.  Augustus  Wing. 
Am.  Jour.  Sci.,  ser.  m,  vol.  13,  1877,  p.  347. 

James  D.  Dana :  On  the  relation  of  the  Geology  of  Vermont  to  that  of  Berkshire.  Am.  Jour.  Sci. 
ser.  Ill,  vol.  14, 1877,  pp.  41,  261-263. 

James  D.  Dana:  Note  on  the  Age  of  the  Green  mountains.  Am.  Jour.  Sci.,  ser.  in,  vol.  19, 1880, 
p. 191. 

James  D.  Dana :  On  Taconic  rocks  and  stratigraphy,  with  a  geological  map  of  the  Taconic  region. 
Part  II.    Am.  Jour.  Sci.,  ser.  iii,  vol.  33,  May,  1887,  p.  405,  410. 

James  Hall :  Section  from  Petersburg,  New  York,  across  Greylock  to  Adams,  the  basis  of  remarks  of 
his  at  a  meeting  of  the  American  Association  of  Geologists  and  Naturalists,  between  1839-1844,  both 
unpublished.  See  Am.  Jour.  Sci.,  ser.  ill,  vol.  28, 1884,  p.  311.  "  Prof.  James  Hall  on  the  Hudson  river, 
age  of  the  Taconic  slates." 


s  i 


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3      D- 


MOUNT  GEEYLOCK.  133 

what  is  above  outlined,  probably  because  of  the  wide  reach  of  territory 
covered  by  the  Taconic  belt,  and  the  overshadowing  importance  of  the 
stratigraphic  relations  on  either  side  of  it,  as  well  as  the  imperfection  of  the 
topographic  maps  hitherto  published,  and  jjossibly  because  of  the  somewhat 
rugged  character  of  portions  of  the  mountain. 

The  raisons  d'etre  of  this  report  are:  That  Mount  Greylock,  in  itself, 
offered  one  of  the  best  fields  for  the  study  of  the  relations  of  the  Taconic 
rocks  to  each  other,  and  that  sections  across  it,  when  extended  eastward, 
northward,  and  southward,  cut  the  underlying  and  older  rocks  where  the 
latter  were  being  studied  in  detail  by  the  same  division  of  the  U.  S.  Geo- 
logical Survey;  that  careful  work  here  would  aid  in  unraveling  the  geology 
farther  west  in  eastern  New  York;  that  the  geologic  field  work  has  been 
based  upon  a  more  correct  topographic  map ;  that  the  observations  made 
have  been  very  numerous  (in  all,  1,850),  and  have  been  carefully  recorded 
on  such  a  map ;  that  the  work  has  been  done  in  the  light  of  recent  advances 
in  orographic  science,  notably  of  the  special  investigations  of  Swiss  and 
Norwegian  geologists  into  the  structure  of  metamorphic  rocks;  that  a  large 
collection  of  specimens  has  been  gathered,  illustrating  principles  of  struc- 
ture, from  which  large  thin  sections  have  been  prepared  for  microscopic 
study;  that  the  photographic  camera  has  been  freely  used  in  the  field  as 
well  as  the  study,  and  that  the  lithologic  specimens  gathered  in  the  course 
of  this  structural  work  have  been  subjected  to  optical  examination  by  a 
petrographer.  Prof  Pumpelly  has  also  brought  his  wide  experience  and 
critical  judgment  to  bear  upon  the  supervision  of  the  entire  work. 

PHYSIOGRAPHIC. 

The  Tiorthern  third  of  the  western  portion  of  Massachusetts  is  marked 
by  three  main  parallel  mountain  masses  having  the  trend  common  to  the 
Appalachian  system.  The  most  westerly  is  the  Taconic  range,  the  crest  of 
which  divides  the  states  of  New  York  and  Massachusetts;  the  most  easterly, 
situate  about  ten  miles  east  of  the  New  York  line,  is  Hoosac  mountain,  and 
the  central  one  is  Mount  Greylock.  East  mountain  and  Potter  mountain 
together  constitute  a  fourth  but  subordinate  mass,  connecting  the  Greylock 
mass  with  the  Taconics  farther  south. 

Mount  Gi'eylock  with  its  spurs  forms  a  topographic  unit      It  is  sep- 


134  (IKEEN  MOUNTAINS  IN  MASSACHUSETTS. 

arated  on  the  nortli  from  Clarksburg  or  Bald  mountain,  a  projection  of  the 
Green  mountain  range,  by  an  east-west  valley,  through  which  the  Hoosic 
river  turns  on  its  way  to  the  Hudson;  and  from  that  point  the  Greylock 
mass  rises  2,700  feet  in  a  distance  of  5  miles  to  an  altitude  of  3,505 
feet  above  sea  level,  and  thence  descends  more  or  less  gradually  for  11.^ 
miles  in  a  general  south-southwestern  direction,  dying  out  in  gentle  undu- 
lations Avithin  about  2^  miles  northeast  of  the  town  of  Pittsfield.  On  the 
east  it  is  separated  from  the  Hoosac  range  by  the  alluvial  and  terraced 
valle}''  of  the  Hoosic,  while  on  the  northwest  it  is  divided  from  the  Taconics 
by  the  broad  and  picturesque  valley  of  Green  river,  which  flows  into 
the  Hoosic  at  Williamstown.  On  the  west  and  southwest  it  is  separated 
from  East  and  Potter  mountains  by  the  valleys  and  glens  through  which 
flow  the  headwaters  of  Green  river  on  the  north  and  of  the  Housatonic  on 
the  south. 

The  aspect  of  Mount  Greylock  from  a  point  about  4  miles  south  of 
North  Adams,  on  the  flank  of  Hoosac  mountain,  embraces  the  eastern  side 
of  the  mountain  almost  in  its  entire  extent  (PI.  xii),  and  shows  a  central 
mountain  mass,  of  elongated  but  symmetrical  form,  with  subordinate  masses 
of  similar  shape  and  parallel  trend,  steep,  rocky,  wooded,  and  separated 
from  the  central  ridge  by  areas  of  gently  sloping  cultivated  land.  This  alter- 
nation of  wood  and  meadow  land,  and  the  variety  of  form  and  color  which 
it  produces,  are  striking  features  in  the  landscape,  and,  as  will  be  shown 
farther  on,  have  nmch  geologic  significance. 

The  western  aspect  of  Mount  Greylock,  from  a  point  on  the  Taconic 
crest  west  of  South  Williamstown,  forms  a  marked  contrast  to  the  eastern 
(PI.  xiii).  Hei'e  the  central  crest  is  seen  to  descend  rapidly  about  2^  miles 
south  of  the  summit,  and  then  to  rise  a  few  hundred  feet  again.  This  inci- 
sion in  the  crest  is  better  shown  in  Fig-.  74.  Two  powerful  buttress-like 
spurs  project  from  the  central  mass  westwardly  for  over  2  miles.  Their 
summits  are  but  900  feet  lower  than  that  of  Greylock.  The  northerly 
spur,  Mount  Prospect,  or  Symonds  peak,  is  separated  from  the  southerly 
one.  Bald  mountain,^  by  a  deep  east- west  cut,  called  the  "Hopper."  This 
cut  branches  out  to  the  east  into  four  deep  ravines,  which  penetrate  still 

'  This  Halil  moiiutaiii  should  not  be  ooufouuded  with  Clarksburg  mountain,  which  i.s  sometimes 

called  bv  that  uaine  and  kiiuwii  alsi)  a.s  Oak  hill. 


U.   S.   GEOLOGICAL  SURVEY 


MONOGRAPH  XXIII       PLATE  XIV 


Sb 


Sbp 


^:icuijcile  BaU    Sg. 


Ipper  .Bench-  S</ 


JLoyverSericIi^  Stp- 


SOUTHERN   SUMMIT  OF  MOUNT  GREYLOCK. 
The  southern  summit  of  the  Grey  lock  mass  (Saddle  Ball),  west  side,  from  the  north  foot  of  Sugarloaf  mountam.  New  Ashford,  showing  the  bench  of  arable  land  due  to  the  calcareous  schist  iBellowspipe  limestone  l  and  the  still  higher  bench  in  the  Grey  lock  schist  formation.      From  a  photograph. 


MOUNT  GEEYLOCK.  135 

farther  into  the  mountain,  while  on  the  west,  across  its  mouth,  lies  Deer  hill. 
(Compare  Pis.  xiii  and  xvii  with  the  map,  PI  i.)  The  portion  of  the  western 
face  south  of  these  great  spurs  is  best  seen  from  the  north  end  of  East 
mountain  or  from  the  north  end  of  Sugarloaf  mountain  in  New  Ashford. 
This  shows  (PI.  xiv),  a  few  himdred  feet  below  and  parallel  to  the  central 
crest,  a  very  regular,  horizontal  bench  over  a  mile  in  length,  below  which 
is  a  steep  declivity  followed  by  a  far  wider  and  longer  bench  of  more  or 
■less  open  pasture  land.  (See  also  Fig.  74,  p.  194.)  Below  this  again  the 
base  of  the  mountain  is  deeply  cut  into  by  a  series  of  east  and  west  ravines 
parallel  to  the  Hopper.  The  northern  one  of  these  is  known  as  Goodell 
hollow. 

The  aspect  of  the  Greylock  mass  on  the  south  (PI.  xv)  from  the 
north  end  of  the  Lenox  mountain  range  (known  in  Pittsfield  as  South  moun- 
tain), which  is  about  15  miles  south  of  the  Greylock  summit,  shows  the  pe- 
culiar saddle  shape  of  the  higher  portions  of  the  mass  which  render  the 
name  of  Saddle  mountain  so  appropriate,  and  so  familiar  tlu-oughout  south- 
ern Berkshire  Greylock  summit  (3,505  feet)  and  Saddle  Ball  (3,300  feet), 
about  2  miles  apart,  form  the  two  humps  of  the  saddle,  while  the  inter- 
vening portion  of  the  crest  with  a  southwesterly  bend  descending  to  the 
2,900  feet  contour  forms  its  seat.  This  corresponds  to  internal  stuctural 
features.  This  aspect  also  shows  the  subordinate  ridges  and  spurs  on  either 
side  of  the  mass  as  well  as  the  benches  on  either  side  of  its  higher  portions. 

The  aspect  of  Greylock  from  Clarksburg  mountain  on  tlie  north  shows 
the  central  ridge  with  two  lateral  and  lower  ridges  :  that  on  the  east — Rag- 
ged mountain — separated  from  Greylock  proper  by  the  Notch ;  that  on  the 
west,  forming  Mount  Prospect  and  Bald  mountain,  separated  from  the  cen- 
ter by  a  minor  saddle,  hence  long  ago  also  called  Saddle  mountain,  which 
farther  south  passes  into  the  north-south  gorge  continuous  with  the  Hopper. 
From  the  Coast  Survey  station  on  Mount  Equinox  in  Vermont,  which  is  about 
35  miles  north  northwest,  and  therefore  at  an  acute  angle  to  the  strike 
of  Greylock,  the  saddle  form  of  the  central  crest  appears  much  broader 
(Fig.  30).  On  the  east  of  it  the  top  of  Ragged  mountain  is  seen,  and  on  the 
west  several  of  the  subordinate  masses.^    The  structural  significance  of  these 


'  Prof.  Edward  HitcUcock  in  his  Final  Eeport  on  (be  Geology  of  Massachusetts  (1841,  pp.  229-233) 
gave  a  very  graphic  description  of  Greyloclv. 


136 


(iKEEN  MOUKTAINS  IN  MASSACHUSETTS- 


topograpliic  features  will  be  noticed  at  the  end.  The  area  covered  by  the 
mountain,  as  thus  defined,  measares  16^  miles  by  about  3  J ;  that  is,  about 
63  sqtiare  miles.     If  the  short  intervening  range  of  East  and  Potter  mount- 


OeervMts. 


Greylock  SajCUUeBaU.SugarLoa/:   EasfJvit. 

■^:BenchatSencl.Form.Sbp.  CcUc.Sc/tlst, 


Fig.  30.— Sketch  of  Mount  Greylock,  "  Saddle  mountain,"  north-northwest  side,  from  the  TJ.  S.  Coast  Survey  station,  on 
Mount  Equinox,  in  Vermont,  about  35  miles  distant,  shipwing  the  depression  corresponding  to  the  great  trough  in  the  cen- 
tral syncline,  and  the  bench  .it  the  soutli  end  of  the  mass,  due  to  the  Bellowspipe  limestone  horizon  (shown  by  2  birds) 
Owing  to  the  direction  of  the  view  the  mountain  appears  much  foreshortened. 

ains  be  included  (and  structurally  it  belongs  to  the  Greylock  mass),  the' 
mountain  area  would  measure  about  85  square  miles. 

STRUCTURAL. 

This  entire  area  consists  of  a  few  kinds  of  metamorphie  rocks:  lime- 
stone, more  or  less  crystalline  and  micaceous,  quartzite,  and  schists — 
chloritic,  feldspathic,  pyritiferous,  plumbaginous,  calcareous.  In  the  val- 
leys, and  along  the  lower  and  less  inclined  portions  of  the  hills  these  rocks 
are  covered  with  drift. 

The  key  to  the  geologic  stracture  of  Mount  Greylock  is  an  under- 
standing of  the  relations  of  cleavage  and  stratification  and  the  relation  of 
these  to  the  pitch  of  the  folds.' 

There  are  large  areas,  sometimes  half  a  mile  square,  where  the  only 
foliation  presented  by  the  outcrops  is  of  secondary  character  and  where  no 


'  Altliouj;!!  Professor  Eaton,  iu  lii.s  .section  of  1820,  imlicates  cleavage  on  the  T.aconic  range,  its 
importance  seems  to  have  been  overlooked  by  his  successors  iu  the  study  of  this  region. 


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MOUNT  GREYLOCK.  137 

trace  of  stratification  can  be  detected.  As  the  cleavage  foliation  in  some 
places  coincides  with  the  stratification  foliation  both  in  strike  and  dip,  in 
others  ag-rees  in  strike  while  differing  in  angle  of  dip,  and  in  still  others 
differs  from  it  in  the  direction  of  both  strike  and  dip,  and,  furthermore,  as 
the  marks  of  stratification  are  not  infrequently  subject  to  purely  local 
changes,  the  whole  matter  is  attended  with  much  difficulty.  This  is  enhanced 
by  the  absence  of  all  outcrops  over  considerable  areas.  Satisfactory  results 
can  be  reached  only  by  accumulating  a  great  number  of  observations, 
rejecting  those  which  appear  in  the  least  doubtful,  and  by  closely  studying 
the  relations  of  the  remainder.  As  a  rule,  the  most  reliable  structural  data 
on  Grey  lock  have  been  obtained  from  outcrops  where  two  different  beds  were 
in  visible  contact,  or  from  a  series  of  related  outcrops  in  all  of  which  both 
cleavage  and  stratification  foliations  were  equally  manifest  and  discordant,  or 
else  from  large  surfaces  of  rock  at  right  angles  to  the  strike,  where  the  general 
trend  of  the  minor  folds  could  be  distinctly  seen.' 

'  The  following  list  includes  impoitant  recent  works  bearing  on  the  subject  of  cleavage: 

Theodor  Kjerulf:  Oni  Stratifikationens  Spor  (traces  of  stratification).  Kristi.ania,  September,  1877. 

A.  Heim:  Mechanismus  rter  Gebirgsbildung,  im  Anschluss  an  die  Keologische  Mouographie  der 
Toedi-Windgiillen-Grnppe.     Basel,  1878. 

A.  Daubree:  Etudes  synthetiques  de  g^ologie  exp<irimentale.     Paris,  1879. 

H.  Clifton  Sorby:  On  the  structure  and  origin  of  noncalcareous  stratified  rocks.  Quarterly 
journal  of  the  Geological  Society  of  T^ondon,  vol.  36,  1880,  p.  72. 

Ed.,Januettaz:  Mdmoire  sur  Ics  clivages  des  roches  (schistosit(5,  longrain),  et  sur  lenr  reproduc- 
tion.    Bulletin  dela  Soci6ti$  G^ologique  de  France,  3rd  ser.,  vol.  12,  1884,  p.  211. 

O.  Fisher:  On  fanlting,  jointing,  and  cleavage.  Geological  Magazine,  new  series,  decade  3,  vol.  1, 
p.  205, 266,  396.    London,  1881. 

A.  Harker:  On  slaty  cleavage  and  allied  rock-strnctures,  with  special  reference  to  the  uiechau- 
ical  theories  of  their  origin.     British  Aasooiiition  Report.     188.5  (1886),  pp.  813-852. 

T.  G.  Bonney:  On  the  inetamorphic  rocks.  Anniversary  address.  Quarterly  .Journal  of  the 
Geological  Society  of  London,  vol.  42,  p.  35.     London,  1886. 

Hans  Reusch :  Geologische  Beobachtungen  in  einem  regional  nietamorphozirten  Gebiet  am  Har- 
daugerfjord  in  Norwegen.  Neuos  Jahrbuch  fiir  Min.,  Geol.  u.  Pal.,  V  Boilage-Band,  Heft  I,  p.  53. 
Stuttgart,  1887. 

Emm.  de  Margerie  &  Dr.  Albert  Heim :  Die  Dislocatiouen  der  Erdriude;  Versnch  einer  Definition 
und  Bezeichnung.     Ziirich,  1888. 

Henry  M.  Cadell:  Experiments  in  mountain  building.  Transactions  of  the  Royal  Society  of 
Edinburgh,  vol.  xxxv,  part  i,  third  series  of  experiments.  Feb.  20,  1888.  Abstract  in  Nature,  vol. 
37,  p.  488.    March  22,  1888. 

Hans  Reusch  :  B0ramelcln  og  Karmoen  med  omgivelser  geologisk  beskrevne.  With  an  English  sum- 
mary of  tlie  contents.     Kristiajiia,  1888. 

T.  Nelson  Dale :  On  plicated  cleavage  foliation.     Am.  Jour.  Sci.,  ser.  iii,  vol.  43, 1892,  p.  318. 

Geo.  F.  Becker:  Finite  homogeneous  strain,  flow  and  rupture  of  rocks.  Bull.  Geol.  Soc.  Am.,  vol. 
4, 1893,  pp.  13-90. 


38 


GREEN  MOLfNTAINS  IN  MASSACHUSETTS. 


Loc.602 


TYPES    OF    STRUCTURE. 

In  order  to  present  this  matter  more   clearly,  a  few  typical  localities 
will  here  be  described  in  some  detail. 

CASE  I. 

On  Quarry  hill,  close  to  the  village  of  New  Ashford,^  there  are  several 

minor  folds  in  the  limestone  and  the  over- 
lying schist,  where  the  two  rocks  may  be 
seen  in  contact.  Fig.  31  represents  the 
structure  at  one  of  these  points  of  contact, 
locality  602  on  sketch  map,  Fig.  78. 

The  banding  in  the  limestone,  the  plane 
of  contact,  the  small  quartz  laminae,  and  the 
general,  slightly  undulating  foliation  in  the 
overlying-  coarse,  feldsjjathic  schist,  all  dip 
in  the  same  direction  at  an  angle  of  about 
30'^."     There  is  little  room  for  doubt  that 


SE. 


'biri'c  mica  schist 


5   ft 


Fig.  31. — Diagrammatie  sketch   .shnwiuji  al 
bitir  schist  iu  eoDformable  cnntai-t  with  iimlcrly 

ing  cry.stamne  limestone,  tbo  foliations  of  both    ^j^g  foHatiou  iu  the  schist  hcrc,  wliatevcr  its 

rocks  (lipping  30^  SE.    Locality  602,  Quarry  hill,  ' 

New  Asbford.  cause,  is  parallel  with  the  stratification,  and 

that  both  rocks  are  conformable.     This  is  the  normal  structure. 

T.  Nelson  Dale:  The  Rensselaer  Grit  Plateau  in  New  York.  Thirteenth  Annual  Report,  U.  S. 
Gcol.  Survey,  1893,  pp.  291-340. 

Of  the  older  well-known  works  ou  this  subject  the  following  are  the  most  important: 

A.  Sedgwick:  On  the  structure  of  large  mineral  masses.  Tran.s.  Geol.  Soc.  of  London,  2nd  ser. 
vol.  3,  183.^,  pp.  fi8,  461. 

Charles  Darwin:  Geological  observations  on  South  America,  lieing  part  iir  of  the  geology  of  the 
voyage  of  the  Beagle.  London,  184r>.  Chap.  vi.  Plutonic  and  metamorphic  rooks;  cleavage  and 
foliation. 

Daniel  Sharpe:  On  slaty  cleavage.     Quarterly  .Journal,  Geol.  Soc.  London,  vol.  3,  1847,  p.  74. 

Henry  Clifton  Sorhy :  On  the  origin  of  slaty  cleavage.  ildinb.  New  Philosophical  Journal,  vol. 
53,  1853,  p.  137. 

John  Phillips:  Report  on  cleavage  and  foliation  in  rocks,  and  ou  the  theoretical  explanations  of 
these  phenomena.     Report  of  British  Association  for  the  Advancement  of  Science,  Part  1, 1856,  p.  .369. 

Henry  Clifton  Sorliy :  On  slaty  cleavage  as  exhibited  in  the  Devonian  limestone  of  Devonshire. 
Philosophical  Magazine,  ser.  iv,  vol.  12,  London,  18.56,  p.  127. 

John  Tyndall:  On  the  cleavage  of  slate  rocks.  Philosophical  Magazine,  ser.  iv,  vol.  12,  London, 
1856,  p.  129. 

Samuel  Haughton :  On  .slaty  cleavage  and  the  distortion  of  fo.ssils.  Phil.  Mag.,  ser.  iv,  vol.  12, 
London,  1856,  )).  409. 

'See  Appendix  H,  Kigs.  77,  78. 

■'All  comjjass  readings  in  this  report  are  cori'ected  for  variation. 


MOUNT  GEEYLOCK. 


139 


CA.SE  II. 

About  150  feet  northeast  of  locality  G02  there  are  two  very  small  folds 
in  the  limestone,  passing  into  a  very  low  southwesterly  dip  on  the  west. 
(See  Figs.  32  and  78.)  In  the  overlying 
plumbaginous  schist  there  are  corresponding 
undulations,  but  these  ai'e  compounded  of 
more  minute  ones  and  crossed  by  cleavage 
planes.  Where  the  plications  dip  50°  south- 
west the  cleavage  planes  dip  40°  to  50°  east. 

Where    the  former  dip   15°   to   20°   southwest  Fig.  32.-Diagraramatic  sketch  of  the  north 

^  side  of  a  lodge  at  locality  297,  on  Quarry  hill, 

the  latter  dip  35°  east,  and,  again,  where  the    now  Ashtowi,  showing  phimbaghious  s.hist  in 

■*-  /  f      CD  f  conformalile  contact  with  unucrlying  crystal- 

former  are  more  nearly  horizontal  the  latter    ""»  "'"'^t'""".  ''"'i  ■''  cleavage  foliation  cross- 

^  ing  the  stratification  ioliation  ot  the  sc^hist  at 

are  vertical.     P'ig.  33,  taken  fi-oni  the  upper    7*™"^  angles. 
portion  of  the  section  (Fig.  32),  shows  the  relations  first  described.    Fig.  34, 

taken  from  a  slightly  enlarged 
])hotograph  of  a  large  section 
of  a  specimen  from  the  same 
portion  of  tlie  ledge,  shows 
more  distinctly  what  is  but 
slightly  apparent  in  Fig.  33, 
namely,  that  the  cleavage 
planes  arise  in  a  faulting  along 
the  shanks  of  tlie  plications. 
In  many  cases  tlie  faulting  is 
only  incipient.  In  a  specimen 
from  the  central  part  of  the 
leda'c  where  the  cleavasfe 
planes  are  ^'ertical  they  are 
simple  joint-like  fractures 
across  the  stratification  folia- 
tion ftf  the  schist,  but  along  one  of  these  faulting  has  occurred,  and  the 
stratification  foliation  is  bent  about  into  the  direction  of  the  cleavage. 

We  have  here,  then,  a  cleavage  which  is  in  jiart  a  microscopic  joint- 
ing, in  })art  what  Heim  has  called  "Ausweichungsclivage"'  (slip  cleavage), 


Fig.  33.— Specimen  in  inverted  position,  facing  south,  from  the 
upper  part  of  thi-  rock  figured  iu  Fig.  32,  locality  297,  Quarry  hill. 
New  Ashford.  PUiiiibagiuous  schist  with  .a  stratification  foliation 
dipping  southwest  about  50°,  crossed  by  a  coarse  cleavage  foliation 
dipping  400-50°  E.    From  a  photograph. 


>  See  Heim,  op.  cit.,  vol.  ii,  ji.  5i,  Gesetz  1,  aurt  Atlas,  PI.  xiv,  Figs.  17, 18 ;  PI.  .xv,  Figs.  T,  8,  9, 11, 14. 


140 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


resulting  in  a  coarse  foliation  crossing  the  stratification  foliation  at  angles 
varying  from  45°  to  90°,  and  abutting  against  the  limestone  which  under- 
lies th.e  schist  in  conformable  contact. 


Fig.  34. — Thin  aection  of  a  specimen  from  tiie  upper  part  of  tbe  rock  tigured  in  Fig.  33.  locality  297,  Quarry  hill,  Now 
Ashfurd,  enlarged  almost  2  diameters,  showing  cleavage  planes  arising  in  slight  faults  along  the  aides  of  the  plications. 
The  fractures  which  occurred  in  the  preparation  of  the  slide  are  mainly  in  tbe  direction  of  the  stratification  foliation, 
which  here  dominates. 

CA.SK  III. 

At  the  south  end  of  Sugarloaf  mountain,  one  of  the  subordinate  folds 
of  the  Greylock  mass,  a  small  isolated  mass  of  feldspathic  schist  over- 
lies the  crystalline  limestone.  (See  map,  PI.  i,  locality  324  and  Fig.  35.) 
Here  limestone  and  schist  are  seen  in  contact,  lioth  distinctly  plicated,  and 


FlQ.  35.— Diagrammatic  sketch  of  the  south  side  of  a  ledge  at  locality  324,  south  foot  of  Sugarloaf  mountain.  New  Ash- 
ford,  showing  albitio  .schist  in  confonnable  contact  with  underlying  cryataUiue  limestone,  and  a  coarse  and  line  cleavage 
foliation  crossing  the  stratification  foliation  of  both  rocks. 

dipping  in  a  general  westerly  direction,  but  really  forming  part  of  a  minor 
fold.  Where  the  stratification  foliation  dips  jGO°  west  it  is  crossed  by 
cleavage  planes  dipping  35°  east,  which  in  places  traverse  both  rocks. 
The  limestone  a  few  feet  away  from  the  schist  appears  in  thick  beds.  Both 
schist  and  limestone  are  traversed  here  and  there  by  coarse  or  fine  cleavage. 


MOUNT  GREYLOOK. 


141 


The  presence  of  both  cleavage  and  stratiticatiun   in  limestone  is  also 
seen  in  a  small  mass  a  little  north  of   this  locality  (Fig-.  '66),   probably 


Fig.  36.~Block  of  limestone  <J  feet  liiyli  ou  the  aoutUweat  fuot  of  Siigarlo<it'  mnuutaiu,  Now  AsliiVird,  showiiij;  a 
coar.se  stratilication  i'oliatiou  dippiuji  to  tlio  riy;bt,  crossed  by  a  tine  cleavage  foliation  dipping  to  tlie  left.  Frtnu  a  photo, 
graph. 

detached  from  some  part  of  the  foot  of  Sugarloaf  mountain,  and  still  more 
strikingly  and  on  a  large  scale  on  the  east  side  of  the  same  mountain, 
(locality  590,  Fig.  37).     The  cleavage  foliation  dips  here  about  20^  east, 


Strat.f  drpbS-W 


Fig.  37 — Sketch  of  the  south  side  of  a  limestone  ledge  at  locality  590,  on  the  east  side  of  Sugarloaf  mountain,  showing  a 
coarsely  plicated  stratilication  foliation  dipping  about  65^^  west,  crossed  by  a  cleavage  foliation  dipping  about  20^  east. 
Area,  25X15  feet. 

and  the  stratification  about  65°  west.     In  some  of  the  neighboring  ledges 
only  the  easterly  dipping  foliation  is  visible. 


142 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


(_)ii  tlie  east  side  of  East  mountain,  near  the  old  marble  quairies  and 
sawmill  (locality  756),  there  is  a  ledge  of  limestone  with  a  thin  lamination 


Fig.  ;i8.— Specimen  from  the  weathered  end  of  a  limestone  ledge  at  locality  756.  east  side  of  East  mountain,  allowing  a 
plicated  stratification  foliation  dipping  to  the  right  and  a  cleavage  foliation  to  the  left.    Photographed  in  inverted  position. 

dipping    25°  to  40°   east.     On    a  closer  examination    the  weathered    end 
of  the  ledge  shows  that  this  is  crossed  by  a  plicated  foliation  dipping  30° 


Fig.  39.— Polished  surface  of  limestone  specimen,  Fig.  38,  in  its  natural  position,  facing  south,  showing  stratification 
dijiping  west  and  cleavage  east.     From  a  iikotograiih. 

to  40°  west.     The  presence  of  a  little  quartz  in  some  of  the  stratification 
planes  makes  the  plications  project  on  the  weathered  surface.     (See  Fig.  38). 


MOUNT  GREYLOCK. 


143 


On  a  polished  .surface  they  can  easily  be  traced.  (See  Fig.  39.)  On  the 
north  side  of  the  ridge,  south  of  the  Hopper,  (locality  899)  the  stratifi- 
cation foliation  is  indicated  by  white  calcite  meandering  through  the 
gray  limestone.  At  a  small  cave  about  two-thirds  of  a  mile  northeast  of 
the  Lanesboro  Iron  Company's  ore  bed  (locality  998)  the  relation  of  cleav- 
age to  stratification  in  limestone  is  also  clearly  seen.  That  the  plane  folia- 
tion is  cleavage  foliation  is  rendered  highly  probable  from  the  usual  char- 
acter and  origin  of  such  foliation'.  There  may  be  cases,  however,  where  it 
would  be  difficult  to  decide  whether  the  plications  in  limestone  are  due  to 
"false  bedding"  or  to  original  stratification. 

From  all  this  it  appears  that  cleavage  phenomena  in  the  Oreylock  area 
affect  both  schist  and  limestone. 


CA.SE  IV. 


In  some  loose  pieces  of  limestone  found  on  Quarry  hill,  New  Ashford, 

1 


F]G.  40.— Loose  piece  of  limestoue  from  Quarry  hill,  New  Ashford,  showinj:  on  the  weathered  surface  laiiiiua^  of 
micaceous  matter  in  both  cleavage  and  stratification  planes.  The  neai'ly  hurizoDtal  lamina'  represent  the  stralitication 
foliation.    From  a  photograph. 

both  cleavage  and  stratification  foliation  are  indicated  by  laminae  of  mica- 

'  Cleavage  foli.atiou  may  be  .subsequently  bent,  but  tliis  rarely  occur,s.  See  Ch.  Darwin,  loo.  cit., 
also  J.  B.  Jukes:  Student's  Manual  of  Geology,  edited  by  Archibald  Geikie,  3.1  ed.,  Edinburg,  1872, 
p.  224,  225.  Dr.  H.  Reuscb  in  his  Geology  of  the  Islaiid.s  of  Bouimelo  and  karnio,  etc.,  already  cited, 
describes  on  p.  196,  Fig.  2,  and  p.  408,  an  interesting  sjiiciuien  from  Foien,  an  islet  .at  the  mouth  of  the 
Hardangerfjord  in  Norway.  The  specimen  figured  shows  both  the  original  stratiiication  foliation 
(jilicated)  and  the  ensuing  cleavage  foliation  (slip  cleav.age),  and  also  the  secondary  plication  of  both 
of  these  foliations,  all  on  a  small  scale.  One  or  two  (ireylock  specimens  show  a  slight  flexure  of  the- 
cleavage  foliation.  Plicated  cleavage  in  the  Taconic  range  at  West  Rutland,  Vt.,  is  described  in  the 
author's  report  on  the  Ren-sselaer  (irit  Plateau  in  the  Thirteenth  Annual  Report  of  the  Director  of 
the  U.  S.  Geological  Survey,  pp.  291-340.     .See  also  A.  Baltzer,  op.  cit.  (p.  152),  pi.  xui,  tig.  11. 


144 


GKEEN  MOUNTAINS  IN  MASSACHUSETTS. 


ceous  iiuitter  wliieli  })r(iject  ou  the  weathered  «urt';u-e.  (See  Fig-.  4U).  These 
.specimens  clearly  indicate  iutiltration  and  inetaniorphisni  subsequent  to 
cleavage. 

CASE  V. 

The  stratification  foliation  and  tlie  cleavage  foliation  are  both  some- 
times minute  in  the  schist  and  equally  dominant.  Fig.  41  represents  such 
a  specimen  from  Bald  mountain  on  the  west  side  of  Greylock. 


^"" 


'■% 


.'9S(J'S7 


/ 


Inth 


!FlG.  41. — .S]ieciineu  of  schist  frutu  lucaiity  95  uu  B.-ild  moun- 
tain, west  side  uf  Greylock,  nut  in  natural  pnsitinn.  showing 
both  stratiticatiun  and  cleavage  foliations  somewhat  minute 
and  equally  duiiiiuaul.  Kach  jiair  i.f  ojiposite  sides  of  the 
hloclv  is  jiarallel  to  one  of  the  foliations,  cleavage  dips  to  the 
loft.     From  a  photograph. 


Flu.  42.— Specimen  of  schist  from  local- 
ity 621,  north  end  of  Mount  rrospect,  in 
natural  position,  facing  south,  showing 
only  cleavage  foliation  dipping  50^  east. 


Fig.  42  represents  a  specimen  from  Mount  Prospect  in  which  only 
cleavage  planes  dipping  50°  east  are  visible  to  the  naked  eye.  Under  a 
magnifying  glass  the  stratihcation  foliation  barely  appears  in  minute  crinkles 
crossing  the  cleavage  planes,  but  the  cleavage  foliation  dominates.  These 
crinkles  come  out  more  clearly  in  an  enlarged  section  (Fig.  43)  and  indicate 
a  westerly  dip,  which  is  confirmed  by  observations  on  some  of  the  neigh- 
boring ledges,  where  the  stratification  foliation,  marked  by  small  plicated 
quartz  lamina?  visible  to  the  unaided  eye,  dips  at  a  high  angle  west.     Simi- 


MOUNT  GREYLOCK. 


145 


larly  some  of  the  schists  on  Bald  mountain,  near  where  specimen  d5d  (Fig. 
41)  was  obtained,  sliow  notliino-  but  cleavage  planes,  and  even  under  the 


Fig.  43. — Tliiu  stM-tion  ol'  part  ol  Mpecimeu,  Fig.  42,  euluri^t-d  2^  diameters,  showiug  a  minute,  plicated  stratification 
foliation  crossing  a  tine  cleavage  foliation.  Fractures  in  preparing  alide  took  place  along  the  cleavage  which  here  (iomi- 
nates. 

microscope  barely  reveal  the  other  foliation.  The  structural  character  and 
relations  of  these  foliations  appear  in  Figs.  44  and  45,  which  show  how  the 
crinkling,   and  sometimes  the  exceedingly    minute  faulting  of  the  small 


Fig.  44. — Thin  section  of  .a  sitcciiiien  of  wchist  from  near  the  top  of  Mount  Grcylocii,  enlarged  2\  diameters,  showing 
the  (levelopnieut  of  slip  cleavage  from  tlie  crinkling  of  the  laminre  of  quartz  and  loUa  of  mica  and  chlorite.  Tlie  fracture 
on  the  right  follows  mainly  the  direction  of  the  cleavage.    From  a  photograph. 

laminne  of  quartz   and  folia  of  muscovite   and  chlorite   of  the  stratification 
foliation  produce  cleavage  planes.     The  schists  of  the  Taconic  range  show 
these  foliations  on  a  still  more  minute  scale, 
MON  XXIII 10 


146 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


These  facts  indicate  that  stratiiication  fohatiou  aud  cleavage  foUation 
may  be  equally  or  uuequally  dominant  or  microscopic. 


Fig.  45.— Microsccijiir  drawing  of  .ibout  i  inch  square  of  a  tliin  section  of  a  specimen  of  schist  from  locality  741,  on 
East  mountain,  culargcnicut  :i9  diameters.  The  light  portions  are  mainly  quartz,  the  dark  mainly  sericite  and  chlorite. 
The  central  plication  shows  the  development  of  cleavage  from  a  slight  crinkling  to  a  complete  fault.  Another  cleavage 
plane,  about  J  of  a  millimeter  to  the  right,  contains  some  ferruginous  matter. 

CA.SE  VI. 

Frequently  small  lenticular  masses  or  laminae  of  quartz  of  irregular 
thickness  occur  in  the  schists.  Their  form  and  direction  are  sometimes  so 
irregular  as  to  give  no  information  as  to  structure,  but  they  sometimes  show 
a  general  parallelism  either  to  the  cleavage  foliation  or  to  the  stratification 
foliation  or  to  both.  Fig.  46  represents  a  specimen  from  locality  550,  about 
1,500  feet  south  and  500  feet  below  the  Greylock  tower. 

The  specimen  consists  of  two  parts,  a  mass  of  schist  about  3  inc"hes 
thick,  capped  by  a  quartz  lamina  about  a  half-inch  thick,  which  undulates 
conformably  to  the  general  stratification  foliation  of  the  schist.  The  strati- 
fication foliation  dips  west  at  a  very  low  angle,  while  the  cleavage  foliation 


MOUNT  GREYLOCK. 


147 


dips  60°  east.  Within  a  space  of  2  inches  the  schistose  part  of  the  speci- 
men shows  as  many  as  twenty  cleavage  planes  crossing  the  stratification 
fohation,  besides  quite  a  number  of  incipient  cleavage  planes.  Within  the 
same  space  the  quartz  is  traversed  by  nine  to  ten  fissures  which,  although 
not  always  continuous  with  the  cleavage  planes  of  the  schist,  yet  preserve 
their  general  direction.  All  the  minute  undulations  in  the  schist  are  gen- 
eralized in  the  quartz.  This  is  also  shown  in  a  specimen  from  the  west  side 
of  Deer  hill.  Here  there  are  two  undulating  quartz  laminae  generally  par- 
allel to  each  other.     While  the  thicker  one  makes  an  S-shaped  curve,  the 


Fig.  46. — Specimen  of  schist  from  locality  550,  about  J  mile  soutli  of  Greylock  summit,  in  natural  position,  showing  in 
upper  part  a  quartz  lamina  about  i  incli  thick,  conforming  to  the  general  course  of  the  minute  plications,  which  dips  west 
at  a  low  angle  while  the  cleavage  dips  60°  east.    From  a  photograph. 

thinner  one  is  plicated  in  the  same  distance  as  many  as  nine  or  ten  times. 
As  geologists  have  observed,  such  coarse  quartz  laminae  in  schist  often 
run  parallel  to  the  cleavage  foliation.  In  order  to  arrive  at  their  true  strati- 
graphic  significance,  not  only  should  their  general  dip  over  a  large  surface 
be  noted,  but  allowance  should  be  made  for  their  passing  into  the  cleavage 
foliation  for  any  considerable  distance,  especially  when  the  dip  of  that 
foliation  forms  a  considerable  angle  with  that  of  the  stratification  foliation. 
Fig.  47  illustrates  the  relation  of  quartz  lamiufe  to  the  cleavage  foliation. 
The  cleavage  here  dips  about  50°;  the  lamijise  in  a  few  places,  and  for  short 


148 


GBEEN  MOUNTAINS  IN  MASSACHUSETTS. 


distauees,  dij)  at  the  same  angle,  but  vary  from  30°  to  90°,  while  their  gen- 
eral dip  ranges  from  40°  to  80°;  and  the  stratification  dip  lies  between  those 
extremes,  being  probably  higher  than  the  cleavage  dip.     If  it  could  be  shown 

that  such  laminte  are  infiltrations  in 
fissures  following  alternately  either  of 
the  foliations,  those  portions  of  the  lam- 
inae which  do  not  follow  the  cleavage 
foliation  would  alone  afi^ord  reliable  in- 
dications, but  if  their  occasional  paral- 
lelism to  the  cleavage  foliation  repre- 
sents parts  of  the  course  of  the  stratifi- 
cation their  general  dip  should  be  taken. 
At  locality  207,  near  the  junction 
of  Grulf  brook  and  Ashford  brook,  there 
is  a  large  ledge  of  schist  which  shows  very  finely  the  relations  of  these  pli- 
cated thick  quartz  liands  to  both  the  stratification  and  cleavage  foliations. 
Fig.  48  represents  the  south  side  of  the  ledge.  The  minute  plications 
(stratification)  of  the  schist  and  of  the  thin  quartz  laminae  ai-e  generalized 


Fig.  47. — Quartz  Limiuie  in  relation  to  cleavage  in 
schist,  from  locality  12G,  south  of  Deer  hill. 


Fig.  48.— South  side  of  schist  ledge,  locality  207,  .junction  of  Gulf  and  Ashford  brooks,  showing  the  relation  of  the 
general  di|i  of  the  ijuartz  lamina-  to  the  minute  plications.  This  dip  is  60°  to  70°.  The  cleavage  foliation,  which  includes 
a  thick  quartz  lamina  below,  dips  35°.    Area  14x10  feet.     From  a  photograph. 

in  the  broader  undulations  of  the  thick  quartz  laminae  which  have  an  aver- 
age dip  of  60°  to  70°.  There  is  also  a  well-marked  cleavage  foliation 
dipping  35°  in  about  the  same  direction.     The  cleavage  planes  do  not 


MOUNT  GREYLOCK. 


149 


traverse  tlie  thick  quartz  laminae.  Microscopic  sections  across  both  schist 
and  quartz  show  the  pai'allehsm  of  the  minute  phcations  of  the  schist 
with  the  adjoining  quartz,  and  the  cleavage  planes  of  the  former  terminating 
at  the  quartz.  There  is  at  least  one  thick  quartz  lamina  in  and  parallel 
to  the  cleavage  foliation.  Through  a  large  part  of  the  more  micaceous 
portion  of  the  ledge  no  stratification  foliation  is  visible  to  the  naked  eye 
or  under  the  magnifying  glass;  and  even  under  the  microscope  the  mass 
shows  only  a  wedge-shaped  structure,  all  the  minute  folia  lying  with 
their  axial  planes  either  parallel  to  the  cleavage  foliation  or  at  a  very  acute 
angle  to  it. 


Fig.  49.— Southwest  and  part  of  south  side  of  schist  ledge  (Fig.  48),  showing  the  relation  of  the  two  foliations.    Area 
15x8  I't.    From  a  }>hotograph. 

Fig.  49  represents  the  southwest  side  of  the  same  ledge,  together  with 
a  portion  of  its  southern  side,  and  also  shows  the  relations  of  the  two  folia- 
tions. The  behavior  of  the  cleavage  and  stratification  foliations,  when  in 
proximity  to  a  thick  quartz  lamina,  is  beautifully  shown  in  Fig.  50,  which 
represents  a  section  from  a  specimen  from  locality  184,  in  Goodell  hollow. 
The  general  parallelism  of  the  coarse  quartz  lamina  to  the  minute  plications 
in  the  schist  on  either  side  of  it  and  the  cleavage  planes  arrested  by  the 
quartz  will  be  observed.  The  longitudinal  cracks  in  the  quartz  are  pos- 
sibly due  to  strain,  as  are  also  the  transverse  cracks  in  the  quartz  lamina  in 
Fig.  40. 

These  facts  indicate  that  the  dip  of  the  stratification  foliation  may  be 


150 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


shown  by  the  general  dip  of  the  thick  quartz  laminae  when  such  lannnte 
can  be  distinguished  from  cleavage  foliation  quartz  larainfe.  Locality  207 
furthermore  shows  that  stratification  foliation  may  be  so  completely  oblit- 
erated that  cleavage  foliation  alone  is  determinable. 


Fig.  50.— Thin  section  of  aericite-chlorite-schist  traversed  by  a  coarsely  plicated  quartz  lamina,  from  locality  184, 
Goodell  hollow,  enlarged  2  diameters,  .showing  the  relation  of  tlie  cleavage  to  the  quartz.  lu  preparing  the  slide  fractures 
have  occurred  along  cleavage  planes.    From  a  photograph. 


CASE   VII. 


On  the  southwest  side  of  Bald  mountain,  locality  242,  the  schist  is 
traversed  by  two  sets  of  foliations  with  different  strikes  The  stratification 
foliation,  distinguished  by  its  plications,  and  in  part  by  the  continuity  of 
the  mineral  constituents  of  the  lamina?.,  strikes  north  40°  to  50°  east, 
and  dips  60°  southeast.  The  cleavage  foliation  strikes  north,  and  dips 
35°  to  40°  east.  The  correctness  of  this  observation  is  coiToborated 
by  one  at  locality  95,  on  the  northern  face  of  Bald  mountain,  about 
4,000  feet  nearly  in  the  direction  of  the  stratification  strike  as  thus  deter- 
mined. There  the  stratification  foliation  is  indicated  by  great  sheets  of 
quartz  striking  north  45°  east,  and  dipping  about  75°  southeast,  corre- 
sponding to  the  minute  plications  in  the  sun-ounding  schist,  which  are 
crossed  by  a  cleavage  foliation  striking  north  3°  to  5°  east,  and  dipping  55° 
east.  The  probable  correctness  of  both  these  observations  is  still  further 
increased  by  the  trend  of  the  central  ridge  of  Greylock,  which,  southeast  of 


MOUNT  GEEYLOCK. 


151 


those  localities,  is  also  northeast.  A  large  ledge  of  schist  at  Readsboro, 
ill  Vermont,  in  the  Grreeii  mountain  range  (Fig.  51),  shows  on  a  large  scale 
the  two  sets  of  foliations  and  quartz  laminse,  with  diiferent  strikes  and  dips, 
and  will  serve  to  illustrate  what  is  not  uncommon  on  Clreylock  in  similar 
rocks. 

The  parallelism  between  the  strike  of  the  cleavage  and  the  strike  of 
the  axis  of  the  great  folds  has 
long  been  recognized  in  geology 
When,  therefore,  the  axis  of  the 
fold  lies  horizontally  the  strike  of 
the  sides  of  the  fold  will  conform 
to  the  strike  of  the  cleavage ;  but 
when  the  axis  of  the  fold  is  in- 
clined, i.  e.,  when  the  fold  pitches, 
the  strike  of  the  sides  of  the  fold 

Fig.  51. — Sketch  of  west  side  of  schist  ledge  in  Readsboro 
will     not     conform     to     that     of    the      linage,  Tt.,showiii{;  stratiHc-itiou  striking  N.  20°  E,  and  dlp- 

l)ing  250  west,  crossed  liy  cleavage  striking  N.  15°  W.  and  dip- 
cleavasre.        This,      Prof.      Pumpelly       I'™S  55°  east,  with  quartz  laminjB  in  both  foliations.    As  the 

''         face  of  ledge  is  not  parallel  with  the  strike  of  either  foliation 
suggests,  is  the  most    probable  ex-      tlie  app-irent  angles  of  dip  are  not  the  tme  ones. 

planation  of  these  differences  between  the  strikes  of  the  stratification  and 
cleavage.  The  conformity  which  Heim  finds  in  the  Alps  between  the 
strikes  of  the  two  foliations  does  not  hold  here.^ 

case;  VIII. 

In  Goodell  hollow,  locality  175,  southwest  of  Bald  mountain,  there  is 
a  schist  with  three  sets  of  planes  or  foliations,  set  a  striking  north  5°  east, 
and  dipping  35°  to  45°  east;  set  h  striking  north  20°  east,  and  dipping  40° 
east;  set  c  striking  north  80°  east,  and  dipping  70°  north.  An  enlarged 
thin  section  (Fig.  52)  shows  that  the  minute  i^lications  follow  the  direction 
of  set  b,  while  set  a  is  formed  by  a  slip  cleavage  more  or  less  pronounced, 
and  set  c  by  the  infiltration  of  dark  mineral  matter  in  planes,  possibly 
fractures,  traversing  the  other  two  sets  without  altering  their  structure. 
This  interpretation  of  this  locality  is  also  confirmed  by  the  strikes  and  dips 
observed  in  its  vicinity.     At  locality  132,  near  the  west  end  and  on  the 


'  See  his  law  13,  op.  cit.,  vol.  2,  p.  68. 


152 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


south  side  of  the  Bald  mountain  spur,  there"  is  a  small  ledge  in  which  the 
stratification  foliation  dips  35°  west,  the  cleavage  foliation  25°  to  30°  east, 
and  a  secondary  cleavage  horizontally  or  very  low  west.  Some  vertical 
joints  strike  north  to  south  through  all  these  planes. 


Fig.  52— Thin  section  of  sericite-clilorite-schist  from  locality  175,  Gootlell  hollow,  the  larger  figure  enlarged  nearly  2 
diameters  and  the  smaller  ahout  10  diameters,  showing  two  cleavage  foliations  crossing  the  stratification.  In  preparing  the 
slide  a  fracture  has  occurred  along  Cleavage  I.    From  photographs. 

Secondary  cleavage  foliation  occurs  here  and  there  in  the  Greylock 


area.' 


ca-sp:  IX. 


Fig.  53  represents  an  enlarged  section  of  plicated  schist  from  locality 
550,  about  1,500  feet  south  of  the  top  of  Greylock.  The  area  in  the  larger 
and  upper  fragment  measures  1 J  by  J  inches.  The  specimen  from  which 
the  section  was  made  showed,  in  its  original  position  in  the  ledge,  a  stratifi- 
cation foliation  about  horizontal  or  dipping  west  at  very  low  angle,  crossed 
by  a  cleavage  foliation  dipping  60°  east.  From  the  direction  taken  by  the 
breaks,  which  occui-red  in  the  preparation  of  the  slide,  it  seems  probable 
that  in  some  portions  of  the  rock  here  the  cleavage  foliation  dominates. 
Fig.  46  represents  a  hand  specimen  from  the  same  ledge  in  its  natural  posi- 

'  Two  sets  of  cleavage  planes  are  uotlced  in  the  slate  on  Welden's  island,  Lake  Champlain.  Geol. 
Report  Vermont,  vol.  1,  p.  314.  A.  Baltzer,  in  the  Beitriige  zur  geologisohen  Karte  der  Schweiz  (20te 
Lieferung,  Bern,  1880.  Atlas,  pi.  m,  fig.  8,  and  xiii,  figs.  14,  16)  figures  two  cleavage  foliations 
traversing  the  same  rock.  Archibald  Geikie,  in  his  report  on  the  recent  work  of  the  Geological  Survey 
in  the  northwest  highlands  of  Scotland,  describes  a  double  foliation  in  eruptive  gneiss.  Quart.  Jour. 
Geol.  Soc,  London,  vol.  44,  Aug.  1888,  p.  398-400. 


MOUNT  GREYLOCK. 


153 


tion.  The  same  stratification  foliation  and  cleavage  foliation  dips  recur  at 
locality  549,  some  2,500  feet  south-southeast,  and  at  locality  539  (see  Fig.  54) 
about  1,000  feet  west,  and  again  at  the  top  of  Greylock,  and  may  thus  be  said 
to  characterize  the  entire  eastern  portion  of  the  summit  of  the  mountain.  If, 
therefore,  the  larger  microscopic  specimen  in  Fig.  53,  which  only  measures 
1^  by  J  inches,  be  properly  oriented  it  will  correctly  represent  the  structure 
of  an  area  measuring  about  two-thirds  of  a  square  mile,  and  probably  the 
entire  east  side  of  the  highest  syncline  of  the  Gi-eylock  mass.  (See  Sec- 
tions G,  H,  I,  PI.  XX.) 


Fig.  53.— Thin  section  of  sericite-iihlorite-schiat  from  locality  550,  about  one-quarter  mile  south  of  Greylock  summit, 
enlarged  2^  diameters,  sliowinj;  a  coarse  slip  cleavajie  crossing  a  very  minutely  plicated  stratification.  In  preparing  the 
slide  fractures  occurred  mainly  in  the  direction  of  the  cleavage,  here  the  direction  of  least  resistance.     From  a  photograph. 

The  microscopic  structure  thus  often  epitomizes  the  general  structure 
on  one  side  of  a  fold.  This  fact  agrees  with  the  drift  of  what  Mr.  Heim 
implies  in  regard  to  the  structure  of  the  Toedi-Windgaellen-Gruppe  namely, 
that  physical  causes  have  transformed  great  masses  by  transforming  the 
minute  particles  which  constitute  them.'     This  generalization  must  not  be 


'  Op.  cit.,  vol.  II,  p.  99. 


154 


GKEEN  MOUNTAINS  IN  MASSACHUSETTS. 


carried  too  far,  however,  for  local  changes  may  occur  for  a  brief  space  in  the 
direction  of  the  plications  and  of  the  cleavage  foliation,  owing  to  the  pres- 
ence of  quartz  nodules ;  or  there  may  also  be  minor  undulations  on  the  side 
of  a  great  fold. 


Fig.  54.— Specimen  of  schist  from  locality  539,  about  one-quarter  mile  .southwest  of  Greylock  summit,  in  its  natural 
position,  facing  south.    Stratification  nearly  horizontal ;  cleavage  dip  500-50°  east.    From  a  photograph. 


CASE  X. 


Loc.576 


Schist 


The  above  cases  are  sufficient  to  illustrate  the  structural  significance 
of  stratification  and  cleavage  and  the  distinction  between  them  in  the  region 
under  investigation.     With  the  aid  of  these  a  fault  was  detected  which 

would  otherwise  have  escaped  notice.  Near 
the  west  end  of  the  Bald  mountain  spur  there 
is  a  somewhat  lenticular  area  of  limestone 
trending  north  and  south,  and  in  contact  on 
both  sides  with  schist.  On  the  west  side  the 
contact  phenomena  are  as  indicated  in  Fig. 
55.  The  limestone  overlying  the  schist  dips 
from  45°-60°  east,  the  contact  plane  between 
both  55°  east;  the  schist  cleavage  dips  25°- 
55°  east,  but  the  plications  in  the  schist  dip 
tvest  at  a  somewhat  higher  angle.  The  nor- 
mal position  of  this  limestone  is  under  the  schist;  here  it  is  above  in  conse- 
quence of  a  fault.  At  this  point 'the  stratification  foliation  in  the  schist  is 
very  much  plicated,  and  the  cleavage  faulting  divides  up  the  rock  into  lens 


Cleavage 
dip.  East. 


Fig.  55. — Diagram  showing  the  relations  of 
the  Beikshire  schist  and  Stockbridge  limestone 
at  locality  576,  on  the  Bald  Mountain  spur,  look- 
ing north.  The  cleavage  of  the  schist  conforms 
to  the  stratification  of  the  limestone,  but  the 
stratifications  are  unconformable. 


MOUNT  GREYLOGK, 


155 


or  wedge-shaped  masses.  This  is  the  typical  slip  cleavage.  The  minute 
structure  at  the  contact,  as  seen  in  a  microscopic  section,  corresponds  to 
that  represented  in  the  diagram.  Fig.  55.  The  inference  from  such  facts 
is  that  while  conformable  contacts  are  all-important  in  determining  strati- 
graphic  relations  in  a  metamorphic  region  they  may  be  entirely  misleading 
unless  it  can  be  shown  that  the  foliations  which  conform  to  the  plane  of  junc- 
tion between  both  rocks  are  indeed  stratification  foliation.' 

CORRELATION   OF    CLEAVAGE   AND    STRATIFICATION. 

The  facts  adduced  naturally  raise  the  question  as  to  the  general  cor- 
relation of  cleavage  and  stratification.  The  relations  of  the  strikes  of  the 
two  foliations  have  already  been  explained  under  Case  vii.     As  to  the  dip 


Fig.  56. — Thin  Bection  of  schist  from  locality  115,  on  the  Bald  Mountain  spur,  enlarged  lA  diameters,  showing  the  paral- 
lelism hetween  the  cleavage  planes  and  the  axial  planes  of  the  plications.    From  a  photograph. 

of  the  two  foliations:  The  range  of  the  difference  in  angle  of  dip  between 
cleavage  foliation  and  stratification  foliation  in  sixty-three  observations  was 
found  to  be  from  10°  to  120°;'  the  average  difference  62°,  30'.  The  abso- 
lute dip  of  cleavage  in  ninety-six  observations,  in  which  the  dip  of  stratifi- 
cation foliation  was  also  observed,  ranged  from  10°  to  90°,  averaging  about 
45°;  leaving  out  eleven  extreme  cases  the  range  was  from  25°  to  75°,  and 
the  average  44°.^  The  direction  of  the  dip  of  the  primaiy  cleavage  in  one 
hundred  and  nineteen  localities,  in  which  that  of  the  stratification  was  also 
determined,  was  distributed  as  follows:  ninety-two  localities  east  or  north- 
east, twelve  west,  four  vertical,  one  south.     The  southerly  dip  occurs  at  the 

•  Compare  J.  D.  Dana,  Taconic  rocks  and  stratigraphy.  Am.  Jour.  Sci.,  Ser.  ill,  vol.  33,  May,  1887, 
p.  398,  in  ■which  the  possibility  of  such  cases  as  this  is  overlooked. 

■^Wben  the  difference  is  over  90°  the  direction  of  the  two  dips  is  opposite. 

'Where  cleavage  is  horizontal  and  stratification  nearly  or  quite  vertical,  as  is  sometimes  the  case 
in  the  Berkshire  county  schist,  there  have  probably  been  two  uplifts. 


156 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


Cleavage 
dip  East 


W.H.H. 


north  foot  of  Mount  Prospect  (Saddle  mountain)  where  there  is  a  well  marked 
southerly  pitch.  The  westerly  dips  occur  in  one  of  the  subordinate  schist 
masses,  which  forms  a  high  cliff  west  of  Cheshire  reservoir,  and  again  in  a 

low  knoll  of  schist  at  the  extreme  sotith  limit 
of  the  map,  near  Berkshire  village,  and  in  a 
similar  knoll  south  of  Constitution  hill  and 
west  of  Lanesboro.  Besides  these  there  is 
one  isolated  observation  between  Lanesboro 
and  New  Ashford,  and  two  others  on  Ragged 
mountain.  So  that  the  observations  indicate 
an  almost  universal  easterly  cleavage  dip  on 
Greylock. 

The  question  may  well  be  asked  how 
this  can  be,  since  the  cleavage  is  so  largely 
associated  with  the  faulting  of  minute  plica- 
tions in  strata  which  sometimes  dip  east  and 
sometimes  west.  The  observations  indicate 
that  where  the  sides  of  a  fold  dip  in  a  direc- 
tion opposite  to  that  of  the  cleavage  the  axial  planes  of  the  small  plications 
are  generally  parallel  to  the  cleavage  planes,  and 
in  extreme  cases  the  faulted  limbs  of  the  plications 
lie  in  those  planes  (see  Fig.  56).  Fig.  57  represents 
this  structure  dia  grammatically,  as  drawn  in  the  field. 
Where  the  cleavage  foliation  and  stratification  folia- 
tion both  dip  in  the  same  direction,  but  at  different 
angles,  the  structure  described  in  Figs.  56,  57  does 
not  occur,  and  the  slip  cleavage  planes  are  then 
either  parallel  with  one  or  with  neither  of  the  limbs 
of  the  plications  as  in  Fig.  59,  or  else  there  is  a  com- 
bination of  an  extreme  form  of  slip  cleavage  bor-       ,,    ^„   T^•         ^     .  ,     ^^ 

t:  a  FiQ.  58.— DL-igram  of  p,art  of  north 

derinff  on  slaty  cleavage  and  of  the  coarse  structure,    "If  "^ '"'""'  'r'^"'  ''"'^"'^'  ^"'  ""'* 

o  J  o  ^      side  ot  Deer  lull,  area 7x5  feet,  show- 

described  in  Case  vi,  Fig.  48,  and  seen  also  in  Fig.  58,    *"«  ™"™'y  p""^*"''  i""'^  '^"""* 

*^  o  '       traversing  the  schist,  which  has   a 

in  both  of  which  the  coarsely  plicated  quartz  laminae  ^^^^^^s^  bordering  on  siaty  cleavage. 
are  more  or  less  iudepeudent  of  the  cleavage  foliation.     Or,  the  cleavage 


Fig.  57.— Diagrams  ahowing  the  relation 
of  slip  cleavage  to  stratification  at  locality  55, 
north  side  of  Mount  "Williams,  and  862,  ridge 
south  of  Sugarloaf.  Cleavage  parallel  to  axial 
planes  of  plications. 


MOUNT  GEEYLOCK. 


157 


foliation,  as  such,  may  disappear  altogether,  becoming  merged  in  the  strati- 
fication fohation.  Tluis,  at  the  south  end  of 
Ragged  mountain,  there  is  a  minor  syncHne, 
on  the  east  side  of  which  the  cleavage  has  a 
high  easterly  dip  crossed  by  plications  dipping 
90°,  or  west,  at  high  angle,  while  on  the  west 

. -,  p    .1  •  !•  .1  .        ,-f       i-  r   1-      •  ''"'  5!».— Diagrams  showing  relation    of 

Side  01  this  synclme  the  stratm  cation  tohation    cieavas,.  to  stratification  in  scinstwiure  both 

T  ^»i-n    .        r>/\(-  ^  1  T    ■•        .       1  foliationsdipin  samedirectiou;  cleavagepar- 

dips    25      to    30      east   and   no  distinct  cleavage      allel  to  one  omeither  Umb  of  plication. 

foliation  is  visible.     (See  Fig.  62.) 

PITCH. 

Early  in  the  work  my  attention  was  directed  by  Prof.  Pumpelly  to 
methods  of  detecting  the  pitch  of  the  axes  of  folds.  Observations  of  pitch 
were  made  in  fifty-four  localities  on  Greylock,  East,  and  Potter  mountains. 

In  a  few  places  minor  pitching  folds  are 
exposed,  as  in  the  limestone  at  the  south 
base  of  Sugarloaf  mountain  (Fig.  60). 
But  pitch  was  usually  determined  by  ob- 
serving the  pitch  of  the  axes  of  the  plica- 
tions of  any  part  of  a  fold.  The  angle 
varies  from  5°  to  45°,  but  generally  is  not 
over  30°.  In  one  or  two  instances  it  was  over  45°.  The  correctness  of 
the  method  seems  to  be  verified  by  the  general  parallelism  which  exists 
between  the  minute  and  general  structure  of  these  rock  masses,  and  also 
by  the  opposite  directi(Mi  of  the  pitch  as  thus  determined,  at  the  extreme 
ends  of  the  mountain.' 

STRrC"rURAL   PRINCIPLES. 

From  the  foregoing  data  the  following  structural  principles  may  be 
laid  down  as  applicable  primarily  to  the  study  of  the  .metamorphic  rocks  of 
Mount  Greylock,  and  then  to  a  large  part  of  the  Taconic  region  and  to 
similar  rocks  and  regions. 

'  See,  on  the  siibjeot.  of  pitch,  Geo.  H.  Cook,  Geology  of  New  Jersey,  Newark,  N.  .!.,  1868,  p.  5,5; 
on  the  inclination  of  the  axes  of  the  flexures  in  the  Taconic  region,  J.  D.  Dana,  Taconic  Rocks  ami 
Stratigraphy,  Part  2,  p.  399,  already  cited* 


Fig.  60. — Minor  limestone  folds  with  a  northerly 
l)itch,  south  foot  of  Sugarluaf,  New  Ashford. 
Rock  50X30  feet. 


158  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

Tli«  lamination  in  «cliist  or  limestone  may  be  either  stratification 
foliation  or  cleavage  foliation,  or  possibly  a  combination  of  both.  False 
bedding  occurs  in  limestone  also.  Therefoi'e  the  conformability  of  two 
adjacent  rocks  is  only  shawn  by  the  conformability  of  the  stratification 
foliation  of  both. 

Stratification  foliation  is  indicated  by :  (a)  the  course  of  minute  plica- 
tions visible  to  the  naked  eye,  (b)  the  course  of  the  microscopic  plications, 
(c)  the  general  covirse  of  the  quartz  laminae  whenever  they  can  be  clearly 
distinguished  from  those  which  lie  in  the  cleavage  planes. 

Cleavage  foliation  may  consist  of:  (a)  planes  produced  by  or  coincident 
with  the  faulted  limbs  of  the  minute  plications,  (h)  i)lanes  of  fractm-e  re- 
sembling joints  on  a  very  minute  scale,  with  or  without  faulting  of  the  pli- 
cations, (c;)  a  cleavage  approaching  "slatj^  cleavage,"  in  which  the  axes  of 
all  the  particles  have  assumed  either  the  direction  of  the  cleavage  or  one 
forming  a  very  acute  angle  to  it,  and  where  stratification  foliation  is  no 
longer  visible.     These  forms  may  all  occur  in  close  proximity. 

A  secondary  cleavage,  resembling  a  minute  jointing,  occurs  in  scattered 
localities,  and,  although  not  yet  very  satisfactorily  observed  on  Greylock, 
original  cleavage  foliation  may  become  plicated  by  secondary  pressure. 

The  degree  and  direction  of  the  pitch  of  a  fold  are  often  indicated  by 
those  of  the  axes  of  the  minor  plications  on  its  sides. 

The  strike  of  the  stratification  foliation  and  cleavage  foliation  often 
differ  in  the  same  rock,  and  are  then  regarded  as  indicating  a  pitching  fold. 

Such  a  correspondence  exists  between  the  stratification  and  cleavage 
foliations  of  the  great  folds  and  those  of  the  minute  plications  that  a  very 
small  specimen,  properly  oriented,  gives,  in  many  cases,  the  key  to  the 
structure  over  a  large  portion  of  the  side  of  a  fold. 

STEUCTURAL    TKANSVEESE    SECTIONS. 

On  these  principles  twelve  complete  and  three  partial  transverse  sec- 
tions have  been  constructed  across  the  Greylock  mass;  there  are  also  three 
across  Stone  hill,  to  which  reference  will  be  made  in  Appendix  A.     All  of 


MOUNT  GKEYLOCK.  159 

these  are  oil  the  same  vertical  aud  horizoutal  scale.'  The  first  section,  A, 
crosses  the  north  end  of  the  mass  at  North  Adams;  the  last,  0,  toward  its 
south  end,  between  Cheshire  and  Berkshire  villages;  and  the  others  at  more 
or  less  regular  intervals  between.  See  map  (PI.  i)  for  section  lines,  and 
Pis.  xviii-xxii,  for  sections. 

The  sections  show  that  the  range  consists  of  a  series  of  more  or  less 
open  or  compressed  synclines  and  anticlines,  which,  beginning  near  North 
Adams,  increase  southerly  in  number  and  altitude  with  the  increasing  width 
and  altitude  of  the  schist  area,  and  then,  from  a  point  about  a  mile  and  a 
half  south  of  tlie  summit,  begin  to  widen  out  and  diminish  in  number  aud 
height  until  they  finally  pass  into  a  few  broad  and  low  undulations  west  of 
Cheshire.^  Betvv'een  that  point  and  the  villages  of  Lanesboro  and  Berkshire 
the  folds  become  somewhat  sharper  and  more  compressed,  and  the  schist 
mass  rapidly  narrows.  The  most  comprehensive  and  best  substantiated  of 
these  sections  are  those  two  which,  beginning  near  South  Adams,  cross  the 
central  ridge  north  aud  south  of  the  summit  and  then  follow  the  two  great 
western  spurs  aud  end  near  South  Williamstown.     These  sections  will  now 

be  described  in  detail. 

It 

'  Prof.  E.  Emmons  (American  Geology,  vol.  1,  p.  19)  gave  a  section  of  Greylock  running  from 
Cheshire  harlior,  across  the  summit,  and  Mount  Prospect,  to  Sweet's  Corners  and  Stone  hill. 

Prof.  .James  Halls  section,  from  Petersburg  to  Adams,  made  between  18.39  and  1844,  but  unpub- 
lished, showed  the  synclinal  structure  of  Greylock. 

Prof.  E.  Hitchcock  (Vermont  Report,  vol.  2,  pi.  15,  fig.  5)  gave  a  section  similar  to,  Imt  less 
detailed  than  that  of  Emmons.  Both  of  these  are  drawn  on  a  greatly  exaggerated  vertical  scale,  and 
represent  the  mountain  as  a  simple  syncline. 

Prof.  J.  D.  Dana,  in  his  paper  on  "Taconic  Rocks  and  Stratigraphy"  (p.  405),  reproduces  Emmons's 
aud  Hitchcock's  sections,  and  adds  several  fragmentary  ones  of  his  own.  On  the  east  side,  one  west  of 
Nortli  Adams  (Fig.  47),  another  west  of  South  Adams  (Fig.  44);  on  the  west  side,  one  on  the  west 
flank  of  Mouut  Prospect  and  north  of  the  Hopper  (Fig.  45).  and  another  on  the  south  side  of  tlie  Hop- 
per (Fig.  46);  all  of  whicli  simply  represent  the  relations  of  tlie  schist  to  tlie  limestone  ou  either 
side  of  the  syncline,  along  the  base  of  the  mountain.  In  his  paper  on  the  "  Quartzite,  Limestone,  and 
Associated  Rocks  of  Great  Barriugton,"  etc.  (1873,  p.  273);  and  again  in  his  paper  "On  the  Relation 
of  the  Geology  of  Vermont  to  that  of  Berkshire"  (1877,  p.  263),  he  conjectures  from  the  north  aud 
south  trend  of  part  of  the  ''llojiper"  depression  that  the  Greylock  syncline  comprises  one  or  more 
subordinate  folds. 

-  The  sections  have  all  been  carried  down  to  the  top  of  the  ijiiartzite  which  underlies  the  Stock- 
bridge  limestone.  The  observed  dips  have  also  been  indicated  on  them  to  enable  the  reader  to  dis- 
tinguisli  between  matter  of  actual  observation  and  of  ordinary  induction.  The  cleavage  dips  have 
beensimilarly  indicated,  but  ou  a  separate  Hue,  and  the  cleavage  foliation  has  also  beeu  shown  on  the 
drawings  crossing  the  stratification  wherever  both  were  observed,  but  it  doubtless  traverses  the 
greater  part  of  the  mass. 


160  .    GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


TRANSVERSE    SECTION    G. 


From  the  Huoaic  river  at  Renfrew  milU  (South  Adams)  across  Ragged  monntain,  the  central  ridge,  Symonda 
peak  {Mount  Prospect),  and  the  north  end  of  Deer  hill     See  PI,  xx  and  Fig.  61. 

Between  the  most  easterly  and  the  most  westerly  outcrops  in  the  lime- 
stone ai'ea  along  the  east  foot  of  Greylock  there  is  a  syncline  followed 
westerly  by  an  anticline.  This  is  corroborated  by  observations  about  the 
quarries  a  quarter  of  a  mile  north.  The  well-knt>wn  relation  of  the  lime- 
stone to  the  schists  farther  up  the  mountain  is  not  shown  here,  but  may  be 
seen  on  Section  B,  PI.  xviii,  about  1 J  miles  south  of  North  Adams,  locality 
28,  where  the  limestone,  after  fomiing  a  very  small  anticline,  ruptured  and 
partially  eroded,  dips,  a  few  feet  west  of  it,  at  an  angle  of  15°  to  30°  west, 
conformably  under  the  schist,  both  rocks  striking  north  25°  east. 

Above,  the  Hoosic  valley  limestone  comes  a  mass  of  schist  which 
forms  the  lower,  more  precipitous,  and  wooded  slopes,  and  which,  along  this 


Fm.  61. — Section  G,  J'rotii  the  Hoosic  river  across  Ragged  mountain,  the  Central  ridge,  Synionds  jieali  (Mount  Prospect) 
and  Deer  hill. 

section,  dips  west  at  an  angle  of  about  30°.  Above  these  schists  is  a 
bench  of  arable  land  stretching  for  several  miles  along  the  east  side  of 
Ragged  mountain.  This  mountain  forms  the  higher  portion  of  the  northern 
end  of  the  range  as  seen  from  Hoosac  mountain  (PI.  xii),  but  is  separated 
from  the  central  crest  by  the  "Notch,"  the  south  end  of  whicli  is  called 
the  "  Bellowspipe,"  from  the  prevalence  of  wind  there.  (Bee  PI.  xvi.) 
This  bench  on  the  east  of  Ragged  mountain  measures  about  600  feet  in 
width  and  is  marked  by  outcrops  of  a  micaceous  limestone  which  here  dips 
70°  to  75°  west.  The  bench  seems  to  owe  its  agricultural  value  in  part  to 
the  rapid  decomposition  and  soil-forming  quality  of  this  rock,  and  })robably 
in  part  also  to  the  fact  that  this  more  deeply  eroded  strip  of  the  mountain 
flank  has  formed  a  receptacle  for  sand  and  soil  which  would  have  been 
drained  off  a  steep  slope.  At  several  points  on  tlie  west  side  of  the  bench 
the  micaceous  limestone  comes  in  close  proximity  to  another  mass  of  schist, 
but  the  upper  contact  is  covered  on  this  section.     At  localities  838,  839,  SeC' 


U.   S.    GEOLOGICAL  SURVEY 


MONOGRAPH  XXIII      PLATE  XVI 


SOUTHERN   END  OF  RAGGED  MOUNTAIN. 
Seen  from  locality  190,  about  one-half  mile  south,  showing  the  easterly  dipping  Greylock  schist  (Sg)  in  contact  with  the  Bellowspipe  llnnestone  (Sbp)  on  the  west  side  of  Ragged  nnountain,  and  the  saddle  14  birdsl  due  to  the  erosion  of  the  limestone  anticline  (Sbpl      The  hollow  to  the  left  is  the  Bellowspipe.     The 

pasture  land  on  the  right  corresponds  to  another  area  of  Bellowspipe  limestone.     From  a  photograph. 


MOUNT  GREYLOCK. 


161 


w 


AibiUc  chlar-mtca  Schist 


deavoffe  tUp  43  °^ 
StraUfdip 


Cleayoffe  dip 

^   Sdnv 


tion  E,  PI.  XIX,  both  rocks  dip  west,  and  at  669,  Section  F,  both  are  Hori- 
zontal, the  limestone  underlying  the  schist  in  all  cases. 

In  ascending  the  east  side  of  Ragged  mountain,  over  this  second  mass 
of  schist  only  westerly  dips  are  met,  but  on  Sections  E,  C,  and  again  about 
a  mile  south  of  Section  Gr  (localities  204,  126)  there  are  some  well-observed 
eastern  dips  following  westerly  ones  and  indicating  a  syncliiie,  which,  proba- 
bly being  less  open  at  this  end  of  Ragged  mountain,  escapes  observation. 
Near  the  top  is  a  narrow  belt  of  calcareous  schist  forming  a  north  to  south 
ravine  across  the  ridge  and  connecting  the  limestone  area  of  the  Notch 
with  that  on  the  south.  Beyond  is  a  small,  isolated  schist  area  which 
forms  the  south  end  of  the  top  of  the  Ragged  mountain  ridge.  The  dips 
continue  westerl}'.  In  de- 
scending into  the  Notch 
the  calcareous  schist  re- 
curs, dipping  60°  east  and 
indicating  another  syn- 
cline.  The  syncliue  of 
this  small  schist  area  is 
best  seen  about  a  half  a 
mile  south  of  the  section 
line,  and  has  already  been 
referred  to  on  p.  157.  (See 
Fig.  62.)  On  the  east  side  of  and  close  to  the  schist,  the  calcareous  schist 
(plicated)  dips  90°  and  west  at  high  angle;  the  schist  (feldspathic  and  chlor- 
itic)  is  also  plicated  iu  the  same  direction,  with  a  high,  easterly  cleavage. 
Again,  at  locality  733,  about  500  feet  south  of  the  section,  the  two  rocks 
come  in  contact  with  westerly  stratification  foliation  and  easterly  cleavage. 
On  the  west  side  of  this  schist  area  both  rocks  are  in  contact  in  inverse  order, 
dipping  east  at  a  low  angle.  These  easterly  dipping  beds  of  the  west  side  of 
Ragged  mountain  stand  out  in  prominent  ledges  which  can  be  clearly  seen 
from  the  top  of  a  knoll  (locality  190)  about  half  a  mile  south  of  the  Bellows- 
pipe.  (See  PI.  XVI.)  The  same  syncline  occurs  on  Section  F  and  also  con- 
tinues south  of  Section  Gr,  on  the  knoll  just  mentioned,  in  the  limestone  and 
calcareous  schist  area.  This  limestone  is  very  pyritiferous  in  places;  an 
assay  of  the  pyrite,  said  to  have  yielded  a  small  percentage  of  gold,  led  re- 


2oort. 


Gz/c.mica-schist  ■ 


Fig  62 — Section  of  sniall  syncline  at  south  enil  Ragged  mountain,  showing 
relations  of  tbe  fiiUatinns  in  the  east  limb.  This  section  crosses  lower  part  of 
central  mass  shown  in  PI.  XVI. 


MON  XXIII- 


-11 


162  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

ceutly  to  some  tentative  raining  here.  From  the  occurrence  of  the  small 
belt  of  calcareous  schist  across  the  top  of  Ragged  mountain  and  from  the 
presence  of  a  well-marked  syucline  in  the  western  part  of  the  small  schist 
area,  the  structure  here  has  been  construed  as  consisting  of  two  minor  folds. 

The  section  now  crosses  the  "  Bellowspipe."  Dip  observations  both 
north  and  south  of  the  line  (see  map,  PI.  i),  indicate  an  anticline  here.  The 
contact  on  the  west  side  of  the  Notch  is  covered,  but  along  Section  F  (local- 
ity 709)  the  micaceous  limestone  dips  west,  and  the  overlying  feldspathic 
schists  occur  a  few  rods  west  of  it  with  a  similar  dip.  Some  800  feet  south 
of  this  (Section  Gr,  locality  589),  a  quartzite,  which  frequently  replaces  or 
is  interbedded  with  these  calcareous  beds,  dips  60°  west  ;  and  in  ascending 
the  hill  the  nearest  outcrop  of  schist  (locality  591),  about  500  feet  west,' 
also  dips  west.  The  relations  which  occur  on  the  bench  on  the  east  side  of 
Ragged  mountain  are  thus  repeated  on  the   east  side    of  the    central  ridge. 

The  section  now  crosses  the  schists  of  the  central  ridge  about  1  mile 
north  of  Greylock  summit  and  about  a  half  mile  south  of  Mount  Fitch. 
The  low  westerly  dip  was  observed  at  several  points  along  the  Grey- 
lock  road  north  and  south  of  this  section  and  also  at  831  south  of  Sec- 
tion E.  The  section  then  descends  into  the  north  fork  of  the  Hopper 
depression.  The  high  westerly  dip  occurs  in  the  precipitous  ravine  which, 
beginning  about  a  quarter  of  a  mile  north  northwest  from  the  sunmiit,  finally 
opens  into  the  north  fork  of  the  Hopper.  Along  the  2,100  to  2,200-foot 
contour  and  extending  down  to  about  the  1,900-foot  contour,  on  the  west  side 
of  the  central  crest  and  in  this  north  to  south  portion  of  the  Hopper,  is  a 
belt  of  calcareous  schist  similar  in  character  to  that  on  both  sides  of  Ragged 
mountain,  but  less  calcareous.  Farther  south,  west  of  Saddle  Ball,  this 
rock  passes  into  the  micaceous  limestone.  At  several  points  westerly 
dips  were  found  in  this  belt.  It  does  not  recur  westward  in  this  portion  of 
the  Greylock  area.  From  these  facts  the  central  crest  has  been  construed 
as  a  sjmchne  of  schist  with  a  steep  west  side,  a  gently  sloping  east  side, 
underlaid  by  the  limestone  and  calcareous  schist  of  the  Notch  and  the 
Hopper. 

Mount  Prospect  (Symonds  peak,  see  PI.  xvii),  consists  of  an  anti- 
cline, with  some  minor  undulations  on  the  east  side  and  a  syncline  on 
its  west  face.     This  is  confirmed  by  observations  on  Section  E  and  also 


MOUNT  GREYLOCK.  163 

on  Bald  Mountain,  Section  I,  PI.  xx.  The  presence  of  the  lower  limestone  on 
the  west  face  of  Mount  Prospect  and  of  the  calcareous  schist  belt  in  the 
Hopper,  east  of  it,  indicates  that  its  schists  correspond  to  those  which,  on  the 
east  side  of  the  range,  intervene  between  the  lower  limestone  (Stockbridge 
limestone)  and  the  calcareous  benches.  On  the  west  side  of  Mount  Prospect 
(locality  1020),  near  the  contact  of  the  schist  with  the  limestone,  there  are 
alternations  between  the  two  rocks  probably  due  to  the  erosion  of  some  minor 
folds.^  The  contact  here  with  the  limestone  occurs  along  the  1,600-foot 
contour,  while  at  the  east  end  of  this  section  it  occurs  between  the  1,200 
and  1,300-foot  lines,  a  fact  already  noticed  by  Prof.  Dana. 

Between  the  schist  boundary  on  the  west  side  of  Mount  Prospect  and 
the  Hopper  brook  is  an  area  about  a  mile  wide,  in  the  eastern  half  of  which 
there  are  numerous  outcrops  of  limestone,  but  the  western  half  of  which 
is  covered  with  di'ift.  There  is  however  little  doubt,  judging  from  the  out- 
crops north  and  south  of  the  section,  that  this  area  is  also  underlaid  by 
limestone,  and,  if  so,  that  it  forms  several  minor  folds.  (Compare  Section 
I.)  It  is  in  the  limestone  at  the  foot  of  Mount  Prospect  and  near  the  mouth 
of  the  Hopper  that  Mr.  Walcott  observed  "several  traces  of  fossils,"  one  of 
which,  he  says,  "appears  to  be  the  inner  whorl  of  a  gasteropod  related  to 
Euomplmlus  or  Madurea? 

Along  the  Hopper  brook,  about  a  quarter  of  a  mile  above  its  junction 
with  the  Green  river,  is  a  small  area  of  quartzite  long  ago  noticed  by 
Dewey  and  Emmons  and  a,lso  referred  to  by  Dana.'     In  Emmons's  section, 

'  Such  interbedding  or  minor  folding  near  the  line  of  contact  occurs  also  west  of  Pittsfleld  on 
Hancock  mountain,  in  the  Lebanon  road. 

^  Chas.  D.  Walcott :  The  Taconic  system  of  Emmons,  and  the  use  of  the  name  Taconic  in  geo- 
logic nomenclature.     Am.  Jour.  Sci.,  ser.  iii,  vol.  3.5,  March,  1888,  p.  238. 

'  Dewey :  "  On  the  stream  which  issues  from  the  Hopper  is  areua'cpous  quartz  of  a  slaty  structure, 
which  is  an  excellent  stone  for  sharpening  the  chisels  used  by  stonecutters."  Am.  Jour.  Sci.,  ser.  I, 
vol  1,  1819,  p.  341. 

Emmons :  "  The  outcrop  of  the  quartz  occurs  again  two  miles  south,  near  a  mill  at  the  junction 
of  the  Hopper  creek  and  Green  river.  A  small  part  only  of  the  mass  is  exposed,  dipping  southeast 
and  towards  the  high  range  of  mountains  known  as  Saddle  mountains  and  Greylock."  Am.  Geology, 
vol.  1,  part  2,  pp.  12-13. 

Dana:  "The  quartzite  of  Stone  hill  and  the  quartzitic  mica  schist  of  Deer  hill  in  Williams- 
town  may  be  either  of  the  upper  or  lower  quartzite  formation,  if  judged  only  by  the  facts  the  hill 
presents.  But  the  position  of  these  areas,  in  the  Williamstown  valley,  between  high  ridges  of  hy- 
dromica  schist,  suggests  rather  that  it  is  the  underlying  Cambrian."  Am.  Jour.  Sci.,  ser.  Ill,  vol.  33, 
May,  1887,  p.  410.     . 


164  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

ali'eady  referred  to,  this  quartzite,  interbedded  with  mica  schist,  is  repre- 
sented as  dipping  conformably  under  the  Umestone  of  the  west  side  of 
Mount  Prospect  and  as  separated  from  the  limestone  area  of  the  Williams- 
town  valley  west  of  it  by  a  fault.^  This  he  also  represents  in  another  sec- 
tion (Greology  Second  District,  p.  145,  Fig.  46).  The  outcrop  in  the  river 
dips  about  30°  eastwardly,  but  a  few  rods  southwest  up  the  bank  (locality 
11)  the  quartzite  has  vertical  plications  traversed  by  joints  dipping  south  or 
southwest.  Mr.  J.  E.  Wolff  finds  considerable  detrital  feldspar  in  this  rock, 
which  distinguishes  it  from  the  feldspathic  schists  of  Greylock  that  overlie 
the  limestone  and  ally  it  to  the  Stone  hill  quartzites.  Mr.  Wolff's  report  on 
this  rock  reads  as  follows : 

"Si)ecinien  l()92fl-.  Slide:  a  fine-grained  aggregate  of  quartz  and  feldspar. 
Stringers  of  muscovite  give  to  the  rock  a  schistose  structure.  The  feldspars  occur 
in  irregular,  angular  giains,  part  uiistriated,  part  striated,  part  microcline.  The  mica 
and  quartz  often  so  surround  and  cut  across  these  grains  as  to  suggest  secondary 
origin  of  the  former.  Some  of  the  feldspars  contain  cores  of  twinned  plagioclase 
feldspar,  surrounded  by  a  rim  of  uutwinned  feldspar,  or  else  a  core  surrounded  by  a 
rim  of  feldspar  in  a  different  orieutatiou,  suggesting  perhaps  secondary  enlargement. 
It  seems  probable  that  the  feldspar  in  this  and  similar  rocks  is  clastic  (angular  shape, 
different  varieties  in  same  rock,  etc.)  It  is  noticeable  that  they  do  not  contain  quartz 
and  mica  belonging  to  the  groundmass,  as  the  pori)hyritic  feldspars  of  the  feldspathic 
schists  of  Greylock  often  do,  suggesting  a  difl'erence  in  origin.  Tourmaline  needles 
occur."  ^ 

When  in  addition  to  this  we  take  into  consideration  the  fact  that  2 
miles  south  of  this  l(>cality,  on  Section  1,  there  is  evidence  of  faulting,  little 
doubt  remains  that  these  quartzites  correspond  to  those  of  Stone  and  Oak 
hills,  and  are  not  to  be  considered  as  quartzose  beds  of  the  Deer  hill  schists, 
which  are  evidently  continuous  with  those  on  the  south  side  of  the  Hopper 
and  overlie  the  limestones. 

At  the  Sweet's  Corner  dam,  about  a  third  of  a  mile  north  of  Section  G, 
the  foliation  (stratification  or  cleavage)  of  the  schist  strikes  north  7°  to  12° 

'  Emmons:  "  Along  the  b  se  of  this  mountain  [Proapect]  is  a  fracture  whose  direction  is  nearly 
north  and  south,  and  tlie  limestone  forming  the  valley  was  severed  from  that  of  the  mountain  side  by 
an  uplifting  force."  Report  on  Agriculture,  p.  80.  See  also  Geology  Second  District  N.  Y.,  p.  157,  and 
E.  Hitchcock,  Report  Oeol.  of  Vermont,  vol.  2,  p.  598. 

'^Compare  Appendix  A,  p.  200. 


MOUNT  GREYLOCK.  165 

east,  and  dips  SO'^  to  35°  east.  Immediately  east  of  the  Ijridge  the  land 
rises  40  to  50  feet,  forming  what  is  called  Sawmill  hill.  In  the  schist 
along  the  foot  of  this  hillock  the  cleavage  strikes  north  7°  to  10°  east,  and 
dips  50°  to  60°  east,  but  plications  are  visible  here  and  there,  striking  east 
or  noi-theast,  and  dipping  south  or  southeast.  The  same  is  time  of  the  out- 
crops farther  up  the  hill.  These  observations  are  confirmed  by  those  at 
locality  1098,  at  the  north  end  of  Deer  hill,  along  the  Green  river,  where 
the  schist  plications  dip  45°  southeast  and  are  crossed  by  cleavage  planes 
dipping  40°  east  in  one  place  and  in  another  70°  east.  On  the  top  of 
the  hillock  the  most  northerly  outcrop  is  limestone  with  somewhat  curved 
strata,  striking  north  5°  east,  and  dipping  35°  to  40°  east,  underlaid  30  feet 
west  by  schist,  with  a  foliation  (cleavage)  having  a  like  dip.  About  100 
and  140  feet  south  of  this  limestone  outcrop  there  are  two  small  masses  of  the 
same  rock  with  coarse,  steep  westerly  or  vertical  plications.  These  may  be 
ledges.  From  all  this  it  has  been  inferred  that  the  schists  of  Sawmill  hill, 
instead  of  underlying  the  limestone  as  represented  in  Emmons's  section,  are 
continuous  with  those  of  Deer  hill,  and  overlie  the  limestone;  that  the  super- 
position of  the  limestone  is  the  result  of  an  overturn  and  a  fault  which  have 
caused  the  schist  to  dip  southeast  and  the  really  underlying  limestone  to 
overlie  it  with  an  eastern  dip ;  and  that  this  fault  reappears  southward,  on 
the  east  side  of  Deer  hill,  where  it  has  brought  up  the  Oak  and  Stone  hill 
quartzites,  which  underlie  the  limestone,  to  the  level  of  the  schists  which 
overlie  it,  causing  a  displacement  of  about  1,400  feet. 

The  section  now  traverses  Deer  hill.  On  the  northwest  side  of  the  hill, 
at  the  Grreen  river,  layers  of  calcai-eous  schist  with  blue  quartz  alternate 
with  a  calcareous,  ferruginous  quartzite,  all  dipping  40°  east.  Their  exact 
stratigraphic  position  is  not  determinable,  but  as  they  are  separated  from 
the  Stone  hill  quartzites  by  a  considerable  area  of  limestone,  as  there  is  no 
evidence  of  a  fault  there,  and  as  the  schists  of  Deer  hill  clearly  overlie  the 
limestone  at  localities  7,  8,  and  630  on  the  west,  these  particular  layers  have 
been  regarded  as  representing  simply  a  transition  from  the  lower  limestone 
to  the  lower  schist.  The  portion  of  Deer  hill  traversed  by  Section  G  has 
for  these  reasons  been  construed  as  a  syncline,  with  a  fault  on  its  eastern 
side. 


166 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


TRANSVERSE  SECTIONS  H,  I. 

From  the  Hoosic  river  above  MapU  drove  station  {Soulli  Adams)  across  the  central  ridge,  Bald  mountam, 
a7id  the  south  end  of  Deer  hill,  to  the  Green  river.  Also  Section  H,  across  the  summit  (see  PI.  XX  and 
Figs.  63,  64). 

The  observations  east  of  the  central  ridge  along  this  section  are  few 
and  unimportant.  The  lower  schist  belt  measures  about  half  a  mile  in 
width,  and  the  area  of  the  overlying  limestone  and  calcareous  schist  about 
a  mile  in  width.     The  latter  is  not  overlain  here  by  a  subordinate  mass  of 

schist  corresponding  to  Ragged  mountain,  but  ex- 
tends uninterruptedly,  and  probably  in  a  series  of 
very  gentle  undulations,  up  to  the  base  of  the  cliffs 
which  form  the  east  face  of  Greylock  proper.  The 
contact  between  the  two  rocks,  wanting  on  Section 
I,  can  be  seen  in  Peck's  brook  on  Section  J,  the 
Fig.  63.-croaa-a6ction  H.  calcarcous  schist  Underlying  the  feldspathic,  non- 
calcareous,  micaceous,  and  chloritic  schist,  both  with  a  westerly  dip.  On 
the  face  of  the  cliff,  locality  549,  the  cleavage  foliation  dips  65°  east,  and 
the  stratification  foliation  15°  to  25°  west,  and  low  west  or  horizontal  dips 
prevail  to  the  summit.  (See  Section  H,  and  Figs.  44,  46,  53,  54.)  At  the 
top  of  the  ridge  which  forms  the  seat  of  the  saddle  between  Greylock  and 
Saddle  Ball  and  so  also  just  west  of  the  Greylock  summit  the  dips  are 
high  east.  The  structure  of  the  top  of  the  central  ridge  here  has  thus  been 
construed  as  a  minor  syncline  with  a  steep  east  slope  on  the  west  side  and 
a  gentle  west  or  horizontal  one  on  the  east  side. 

The  section  line  now  descends  a  little  north  of  Shattuck  flats  to  the 

I 


Fig.  64.— Croaa-aection  I. 


south  fork  of  the  Hopper  brook.  The  observations  above  the  flats  are  not 
conclusive,  but  in  the  most  southerly  ravine,  tributary  to  the  south  fork  of 
the  Hopper,  westerly  dips  occur,  as  they  do  also  in  the  ravine  running  north 


MOUNT  GREYLOCK.  167 

northwest  truiii  the  summit,  which  cuts  deeply  into  the  central  crest,  and 
which  has  already  been  referred  to  under  Section  G.  This  west  dip  is  also 
shown  on  Subsection  H.  The  calcareous  schist  belt  is  crossed  again  and 
recurs  south  in  one  of  the  forks  of  Goodell  brook,  in  both  cases  witli  a 
westerly  dip.  All  this  leads  to  the  same  interpretation  as  in  Section  G, 
excepting  that  a  small  anticline  seems  to  intervene  here  between  the  sum- 
mit and  the  calcareous  belt,  the  compressed  syncline  of  the  central  crest 
having  in  it  a  minor  fold  which  does  not  appear  on  Section  G. 

The  section  then  crosses  Bald  mountain.  Here  a  great  surface  of  the 
lower  schists  is  exposed.  A  high  northeasterly  dip  is  well  determined  at 
locality  95  (see  Fig.  41),  and  corroborated  at  locality  242  on  the  southwest 
side  of  the  mountain,  both  with  a  strike  of  north  40°  east  (see  Case  vii,  p. 
150);  and  an  easterly  dip  recurs  high  up  on  the  east  side  of  Mount  Prospect. 
East  of  this  locality  the  dip  is  east  in  places,  but  there  are  probably  minor 
folds  and  much  thickening.  On  Section  J,  PL  xxi,  which  passes  along  the 
south  side  of  Bald  mountain  about  500  feet  below  its  summit,  horizontal  or 
low  west  dips  occm*,  striking  with  the  much  steeper  dips  of  the  top,  and  prob- 
ably representing  the  lower  and  broader  part  of  the  Bald  mountain  syncline. 
East  of  this,  in  the  Goodell  hollow  ravines,  there  are  high  westerly  dips. 
These  facts,  and  the  situation  of  the  calcareous  belt  in  the  Hopper,  have 
rendered  necessary  the  peculiar  construction  seen  in  tlie  section.  Bald 
mountain  thus  consists  on  the  east  of  a  sharp  anticline  turned  over  to  the 
east,  followed  on  the  west  by  a  syncline  which  probably  consists  of  minor 
folds. 

West  of  Bald  mountain,  along  the  spur  between  the  line  of  the  strike 
of  locality  242,  on  the  east,  and  localities  106  and  645  (Hopper),  on  the 
west,  there  is  an  anticline  corresponding  to  the  one  at  the  top  of  Mount 
Prospect  followed  westerly,  between  localities  218  and  217,  by  a  syncline 
corresponding  to  that  on  the  west  face  of  Prospect.  West  of  this  again, 
between  localities  117  and  217,  such  a  succession  of  westerly  dips  occurs 
that  it  has  been  necessary  to  insert  a  conjectural  compressed  syncline  and 
anticline  in  order  to  explain  the  dips  as  well  as  the  absence  of  the  lower 
limestone.  From  the  dips  in  the  limestone  and  schist  in  the  Hopper  on  the 
northern  side  of  the  spur  it  is  probable  that  another  small  anticline  occurs 


168  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

between  localities  1 15  and  117  on  the  spur.  In  fact,  judging-  from  the  many 
alternations  in  the  dip  and  the  absence  of  the  lower  limestone,  the  whole 
spur  west  of  Bald  mountain  seems  to  consist  of  a  series  of  minor  folds  whose 
number  probably  varies  but  slightly  from  that  represented  in  the  section. 
Fig.  56,  p.  155,  represents  a  specimen  from  locality  115  on  this  portion  of 
the  section.  In  constructing  the  section  the  depth  of  the  limestone  has  been 
governed  by  the  angle  of  pitch  along  the  spur  and  the  relations  of  the  Hop- 
per and  Mount  Prospect  (Section  G)  to  Groodell  hollow  (Section  J). 

About  three-quarters  of  a  mile  east  of  that  arm  of  the  Grreen  river 
known  as  Ashford  brook  the  section  crosses  a  hill  known  locally  as 
"  Pine  Cobble."  On  tlie  west  side  of  it  is  a  small  limestone  area  cut  off  by 
schist:  on  the  north,  from  the  Hopper  limestone  area,  on  the  south  from 
the  New  Ashford  limestone  area,  and  on  the  west  from  the  South  Williams- 
town,  limestone  area.  On  the  east  this  limestone  underlies  the  Bald  mountain 
schists  conformably,  l)ut  on  the  west  side  it  is  unconformably  underlaid 
by  schist,  owing  to  a  fault,  the  character  of  which  has  been  partially 
described  under  Case  x,  Fig.  55.  There  would  seem  to  have  been  a  sharp 
ruptured  anticline  here,  the  eastern  limb  of  which,  consisting  of  the  upper 
400  feet  of  the  lower  limestone,  with  the  overlying  schist,  was  thrown  up, 
while  the  western  part  slid  under  the  limestone,  the  break  having  occurred 
along  the  eastern  limb  of  the  anticline  in  the  upper  part  of  the  limestone 
bed.  This  fault  strikes  with  the  fault  along  the  eastern  side  of  Deer  hill  and 
at  Sawmill  hill,  already  described,  and  with  the  one  referred  to  by  Emmons. 
The  displacement  here  can  not  well  be  less  than  500  to  600  feet.  The 
structure  of  the  entire  spur  also  indicates  a  great  deal  of  compression. ' 

West  of  the  fault  the  schist  dips  high  west,  or  80°,  and  on  the  west 
side  of  Deer  hill,  a  little  north  of  this  section,  the  limestone  of  the  South 
Williamstown  A'alley  occurs  in  contact  with  and  under  the  schist,  both 
rocks  dipping  east.  On  the  east  side  of  Deef  hill  the  dips  are  90°,  or  west, 
indicating  a  synclinal  structure  for  the  central  portion  of  that  hill. 

A  small  ravine  skirts  the  west  brow  of  Deer  liill,  the  east  side  of  which 
is  formed  by  a  cliff  of  schist,  the  west  by  a  low  ridge  of  limestone.     At 

'  At  locality  331,  on  west  side  of  Sugarloaf,  about  3^  miles  south  of  this  part  of  Section  I,  there 
is  au  auticline  turned  over  to  the  west,  bringing  the  schists  under  the  limestone;  and  there  are  some 
indications  of  a  fault  between  them,  but  the  evidence  is  not  conclusive. 


MOUNT  GllEYLOCK.  169 

locality  3'J,  a  little  south  of  east  from  South  Williamstowu  village,  the  struc- 
ture of  the  schist  is  fiuely  exposed  (see  Fig.  58),  the  coarse  stratification 
foliation  (plications)  dipping  about  45°  east  with  a  southerly  pitch,  associ- 
ated with  a  cleavage  foliation  dipping  35°  east.  Following  this  ravine 
southerly,  its  sides  gradually  approach  each  other  until  the  two  rocks  are 
finally  found  in  superposition  with  a  westerly  dip. 

The  chief  jioints  of  interest  in  the  remaining  sections  will  be  only 
briefly  referred  to. 

TRANSVERSE    SECTIONS  A-F,    J-O. 

Section  A,  PI.  xviii,  crosses  the  uortheromost  portion  of  the  range  at  North 
Adams,  aud  shows  a  comiiressed  syncliue  turned  over  westward.'  The  actnal  contact 
may  be  seen  about  a  thousand  feet  west  of  the  North  Adams  railroad  depot,  the 
limestone  overlying  the  schist,  both  rocks  striking  north  22°  east,  and  dipping  45° 
southeast.  I  failed  witli  careful  search  to  find  any  (juartzite  outcrops  in  this  part  of 
Greylock,  ulthough  there  are  numerous  bowlders  of  it  which  have  probably  been 
brought  from  Clarksburg  mountain  or  beyond.'  There  is  room,  between  the  lowest 
outcrop  of  quartzite  on  Clarksburg  mountain  and  the  western  side  of  the  steep  portion 
of  the  Greylock  mass  traversed  by  this  section,  for  a  bed  of  limestone  1,400  feet  thick 
dipping  at  an  angle  of  50°,  which  is  the  dip  of  the  schist  at  locality  fll6  (see  map); 
and  none  of  the  measurements  of  the  thickness  of  the  lower  limestone  obtainable  on 
Greylock  Indicate  a  greater  thi(ikness  than  that. 

Section  B,  PL  xviii,  about  a  mile  and  a  half  south  of  North  Adams.  The  limestone 
of  the  Hoosac  valley  and  the  schist  of  Mount  Greylock  appear  here  in  their  normal 
relations.     The  syncline  which  farther  south  consti-  ^ 

tutes  the  central  portion  of  Eagged  mountain  appears ; 
and  there  is  a  second  syncline  west  of  it,  identical  with 
the  one  on  Section  A,  but  open,  aud  also  with  that  on 
the  east  side  of  the  N"otch.  In  the  western  portion  of 
the  section  two  synclines  and  an  anticline  have  been 
conjectured  from  observations  farther  south.  It  will 
be  observed   that  this  section  crosses  the  Greylock  ^'"^'  65— Cross-sections  a,  b. 

mass  below  the  horizon  of  the  upiier  limestone  and  calcareous  schist. 

Section  C,  PI.  xviii,  about  2  mi  es  south  of  North  Adams.    The  calcareous  bench 


'  See  J.  D.  Dana,  Tacouic  Rocks  and  Stratigraphy,  Sec.  47,  p.  405.  Also,  On  the  Quartzite,  Lime- 
stone, etc.,  of  Great  Harrington,  p-  273. 

-  J.  D.  Dana,  On  the  Taconic  Rocks  aud  Stratigraphy,  p.  406:  ■'  A  prolongation  of  it  [the  Clarks- 
burg mountain  quartzite]  appears  to  esteud  south  of  Braytonville  into  the  north  end  of  the  Greylock 
mass,  along  the  ascending  road  (but  chiefly  on  its  eastern  side)  for  a  mile.'' 


170  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

on  the  east  side  of  Rigj,'ed  mountain  appears  with  minor  undulations.  A  well-marked 
syncline  forms  the  top  of  that  mountain ;  on  its  west  side  the  calcareous  belt  is  crossed 
twice  with  an  intervening  tongue  (jf  the  underlying  schist,  necessarily  anticlinal  in 
structure.  At  the  west  end  of  the  section  there  is  what  might  easily  be  mhtalien  for 
imconformnbility  between  the  limestone  and  schist,  a  foliation  in  the  limestone  (at 
localities  1035,  1036).  striking  north  77O-80^  east  and  dipping  250-50°  south,  while 
the  plications  in  the  schist  close  by  and  higher  up  (locality  1038)  dip  westerly  with 
a  southerly  cleavage,  conformable  to  the  foliation  in  the  limestone.  It  is  highly  prob- 
able that  the  fi)liation  in  the  limestone  is  •  cleavage,  and  that  a  stratification  dipj)ing 
west  conformably  to  the  plication  in  the  schist  has  been  obliterated.  This  would 
make  a  syncline  with  the  limestone  underlying,  as  in  the  section. 

Section  D,  PI.  xviii,  nearly  h:ilf  a  mile  farther  south.  The  Ragged  mountain  syn- 
cline continues  with  the  upper  limestone  dipping  under  it.  On  the  north  side  of  Mount 
Williams  there  is  a  bench  circling  around  from  "  Wilbur's  pasture"  (the  saddle  of  this 
Saddle  mountain),  at  the  south  end  of  the  north  to  south  part  of  the  Hopper,  and  con- 
tinuing into  the  Notch.  The  eastern  part  of  this  bench  is  visible  from  tlie  north  end  of 
Ragged  mountain.  Along  this  bench  probably  passes  Formation  Sbp — heie,  however, 
without  any  outcrops  that  are  calcareous,  exceiJt  at  641  and  645  on  the  north-northwest 
side  of  Mount  Williams.  The  presence  of  masses  of  non-calcareous  schist  measuring 
from  a  quarter  to  three-quarters  of  a  mile  in  length  and  several  hundred  feet  wide  on 
the  northeast  side  of  Ragged  mountain  and  on  the  southwest  side  of  Saddle  Ball  in 
the  upper  limestone  and  calcareous  schist,  and  the  fact  that  in  the  Hopper  the  strata 
of  this  horizon  are  much  less  calcareous  and  more  micaceous  than  at  the  south  end  of 
Saddle  Ball  or  in  the  Notch,  and,  finally,  the  iiresence  of  noncalcareous  quartzite  as 
well  as  limestone  in  the  same  horizon  in  the  Notch,  all  indicate  the  very  changeable 
lithologic  character  of  this  horizon.  Furthermore,  the  general  synclinal  structure  of 
the  central  ridge,  the  presence  of  a  calcareous  belt  on  both  sides  of  it,  and  the  similar 
constitution  of  Ragged  mountain,  together  with  the  fact  that  at  both  ends  of  that 
mountain  the  calcareous  belts  are  connected,  and  the  greater  difficulties  involved  in 
any  other  construction  of  the  central  crest,  all  lead  to  the  interpretation  given  in  the 
map,  and  in  this,  as  well  as  the  other  sections.  Section  D  traverses  Mount  Williams  a 
little  south  of  this  belt  of  Formation  Sbp.  The  ba^is  for  the  remaining  features  of  this 
section  will  be  found  largely  in  the  next  one. 

Section  U,  PI.  xix,  crosses  Ragged  mountain,  Mount  Williams,  and  the  north  end 
of  Symond's  peak  (Prospect  mountain).  The  Ragged  mountain  syncline  passes  east  of 
the  top  of  that  ridge.  Along  the  east  base  of  Mount  Williams  a  long  ledge  of  schist 
shows  iilications  dipping  40O-15o  west,  crossed  by  an  easterly  cleavage  dii^ping  60°. 
These  west  dips  on  the  east  side  and  the  higher  westerly  dips- on  the  west  side  of  Mount 
W^illiams  indicate  the  character  of  the  syncline  of  the  central  ridge  seen  farther  south 
on  Section  G.    The  high  westerly  dips  on  the  top  of  Mount  Prospect  (north  end,  or 


MOUNT  GREYLOCK.  171 

Saddle  mouutaiii,  Icjcalities  G19,  621,)  are  coustrued  as  indicating  a  structure  similar  to 
that  on  Section  Gr  on  the  same  mountain,  but  more  compressed.  The  presence  of  an 
area  of  level  arable  land  measuring  about  1,000  feet  square — "Wilbur's  pasture" — at 
an  altitude  of  2,200  feet  above  sea  level  between  the  schist  masses  of  Symonds  peak 
on  the  west  and  of  Mount  Williams  on  the  east,  forjning  the  saddle  of  this  Saddle 
mountain,  and  corresponding,  as  it  does,  to  the  similar  area,  "Shattuck  flats,"  about 
2J  miles  south,  between  Bald  mountain  and  the  central  crest,  at  an  altitude  of  2,500 
feet,  and  also  to  the  calcareous  bench  on  the  western  and  southern  side  of  Saddle 
Ball  between  the  2,200  and  2,500  feet  contours,  together  with  the  occurrence  of  the 
calcareous  belt  between  Wilbur's  pasture  and  Shattuck  flats  in  the  Hopper  ravines, 
all  point  to  a  structural  if  not  to  a  lithologic  similarity.     (See  PI.  xvii.) 

Section  F,  PI.  xix,  is  confined  to  Ragged  mountain.    The  syncline  and  anticline 
observed  about  the  limestone  quarries  between  Zylonite  (Howlands)  and  Renfrew,  on 
the  mountain  side,  appear  here.    The  lower  schists  measure 
only  about  1,000  feet  on  the  east  side  of  Ragged  mountain 
at  this  point.    In  the  centre  of  the  Notch,  locality  032, 
highly  contorted  strata  of  a  feldspathic  quartzite  with  a 
low  southerly  pitch  occur.     The  occurrence  of  a  similar        fig. oe.-Crosssection f. 
rock  is  so  frequent  in  this  belt  that  it  may  be  said  in  part  to  characterize  the 
horizon.' 

Section  J,  PI.  xxi,  south  of  Section  I,  from  a  point  a  quarter  of  a  mile  south  of  Maple 
Grove  station  (South  Adams),  crosses  a  lens-shaped  compressed  syncline  of  the  lower 
schist,  which  is  here  very  graphitic,  as  it  is  frequently  near  the  lower  limestone. 
At  the  contact,  on  the  east  siile,  the  schist  seems  to  inclose  large  lenticular  blocks  of 
the  underlying  limestone.  West  of  the  main  belt  of  the  lower  schist  is  an  area,  nearly 
2,000  feet  wide,  of  a  rock  resembling  the  feldspathic  quartzite  of  the  Notch,  referred 
to  under  Section  F,  but  so  micaceous  as  to  constitute  a  fine-grained  gneiss.'*  The 
strata  dip  west,  and  appear  to  overlie  the  adjoining  schists.  For  these  reasons  this 
area  has  been  considered  as  forming  part  of  the  ui)per  limestone  belt.  The  observa- 
tions at  the  west  end  of  this  section  in  Goodell  hollow  on  the  south  side  of  Bald  moun- 
tain have  already  been  referred  to  under  Section  I.  Dip  observations  taken  at 
different  elevations  indicate  that  the  folds  become  more  acute  in  the  lower  as  well  as 
the  higher  parts  of  the  mass. 

Sections  K,  L,  PL  xxi,  commence  north  and  south  of  Cheshire  harbor.  The  schist 
mass  east  of  Cheshire  harbor  on  Section  K,  which  sends  out  a  tongue  southwards, 
crossed  also  by  Sections  L  and  M,  is  that  represented  in  Emmons's  section  as  under- 
lying the  Hoosic  valley  limestone,  and  corresponding  to  the  schist  of  Sawmill  hi)' 
near  Sweet's  corners.  But  observations  made  by  other  members  of  this  division  of 
the  geological  survey  along  the  base  of  Hoosac  mountain  show  that  this  schist  mass 


'  Mr.  Wolff's  determiiiiitions  of  this  rock  are  given  ou  p.  185  (locality  345). 
•^  See  p.  186,  specimen  from  locality  616. 


172 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


probably  overlies  the  Hoosic  valley  limestone.  Along  set-tious  K  and  L  there  is  dif- 
ficulty in  tracing  the  connection  of  the  upper  calcareous  belts  of  both  sides  of  the 
central  ridge,  owing  to  the  absence  of  outcrops  on  the  west  side  of  Saddle  Ball.  The 
central  ridge  (Saddle  Ball)  there  slopes  ott"  to  the  east  at  an  angle  of  about  10^,  form- 
ing a  bench  which  is  even  less  inclined  than  that  on  the  west  flank  of  the  mountain. 
See  the  view  fi-om  Lenox  mountain,  PI.  xv.  The  conjectural  track  of  Horizon  Sbp. 
which  on  the  map  joins  the  outcrop  of  micaceous  limestone  at  the  south  end  of  Sad- 
dle Ball  ("Jones's  Nose")  with  those  in  Peck's  brook,  Section  J,  has  been  drawn  to 
conform  to  the  strike  and  trend  of  the  central  ridge,  and  to  those  of  the  calcareous 
belt  on  its  west  side.  It  is  based  on  both  structural  and  topographic  considerations. 
(Compare  the  remarks  on  Section  D.)  On  the  west  of  the  mountain  and  about  Gulf 
brook  there  are  calcareous  schists  separated  from  the  upper  calcareous  belt  by  non- 
calcareous  schists.    These  have  been  thrown  into  the  lower  schists  as  probably  repre- 


FiG.  S7.— Cross  sections  J,  K,  L. 

senting  mere  transitions  from  the  lower  limestone  to  the  lower  schist,  such  as  were  ob- 
served at  several  localities  over  small  areas  (Deer  hill,  630;  Lanesboro,  365;  New 
Ashford,  530),  and  are  thus  regarded  as  only  indicative  of  the  proximity  of  the 
lower  limestone. 

In  Section  L  the  opening  out  of  the  compressed  and  overturned  fold  of  the  central 
ridge  into  a  very  broad  and  open  syncline  is  seen.  The  calcareous  belt  of  the  Hopper 
becomes  here  a  gently  sloping  bench  of  arable  land  nearly  a  quarter  of  a  mile  wide, 
once  dotted  with  farms,  and  still  used  for  pasturage.  (See  PI.  xiv.)  The  rock 
becomes  much  more  calcareous,  aud  dips  east  at  a  low  angle  under  the  upper  schists 
of  the  central  ridge,  and  bends  around  eastwardly  between  Saddle  Ball  and 
Eound  rocks,  the  former  consisting  of  the  upper  and  the  latter  of  the  lower  schists. 
The  upper  schists  form  a  cliff  on  the  south  side  of  Saddle  Ball  at  the  incision  in 
the  central  ridge,  which  is  seen  so  plainly  from  the  Tacomic  range  (PI.  xiii),  and 


MOUNT  GRETLOCK. 


173 


from  East  mountain  (Fig;.  74,  p.  194).     Here  the  strata  are  horizontal  or  dip  very  low 

east,  and  are  crossed  by  a  cleavage- foliation,  as  shown  in  Fig.  68.    The  section  passes 

along  the  foot  of  these  cliffs.    The  upper 

bench  of  Saddle  Ball,  shown  in  Section  L  in 

the  upper  schist,  and  also  in  the  views  (PI. 

XIV  and  Fig.  74),  does  not  correspond  to 

any  calcareous  horizon.    A  quarter  of  a  mile 

north  it  measures  about  800  feet  in   width. 

Section  L  has  been  extended  through  East 

mountain,  where  the  strike  changes  to  north 

40°  to  50°  east,  crossing  the  trend  of  the 

hill,  and  a  sharp  syncline  occurs  in  the  schist  with  the  limestone  of  the  Hancock  valley 

dipping  under  it  on  the  west.     This  schist  is  continuous  with  the  lower  schist  of 

the  Greylock  mass,  but  the  outcrops  did  not  yield  further   structural  data.     East 

mountain  seems  to  be  one  of  the  subordinate  folds  of  the  Greylock  synclinorium 

which  would  thus  measure  here  nearly  seven  miles  in  width. 

M 


L,oc.442.     .^^  -_^      ^  -  — 

2  ft    E. 

^^^^^^^a 

^^S^ 

-A^ \\      v'^'A'x   ^ 

\\~ 

_<..3«,  \  '     Cleayoffe.  dzf) -SSE . 

WHH. 

Fig.  68. — Structure  in  schist  in  cliffs  on  south  .side 
of  Saddle  Ball  above  the  Bellowspipe  limestone. 


Fia.  60.— Cross-sectious  M,  N,  0. 

Section  31,  PI.  xxi,  begins  about  midway  between  Cheshire  and  Cheshire  Harbor. 
The  axis  of  the  central  syncline  .seems  to  continue  in  the  lower  schists  across  Round 
I'ocks,  where  a  cliff  about  1,000  feet  long  from  east  to  west  and  150  feet  high  shows 
low  east  dips  at  its  west  end  and  low  west  dips  at  its  east  end.  (See  Fig.  74.) 
East  of  this  point  observations  were  few  and  unsatisfactory.  Farther  west  the  sec- 
tion crosses  Sugarloaf  mountain,  which  is  a  small  open  syncline.  (See  Appendix 
B.)  West  of  it  a  number  of  minor  folds  produce  the  frequent  alternations  of 
schist  and  limestone  about  New  Ashford.  The  entire  synclinorium  here  consists  of 
a  greater  number  of  smaller  folds.  The  section  is  below  the  horizon  of  the  upper 
limestone. 


w. 
lotJI5. 


Quart?  lamina 
Stratif. 


174  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

Section  N,  PI.  xxii,  begins  at  Cheshire  and  shows  a  synchne  in  the  schist  north 
of  the  Farnham's  quarry  limestone  area.  This  syncline  appears  to  be  continuous  with 
that  of  Sections  K  and  L,  and  is  also  on  the  line  of  the  Bagged  mountain  syncline. 
North  of  the  Lanesbort)  limestone  area  there  are  indications  of  an  anticline  in  the 
schist;  and  between  this  and  the  syncline  on  the  east  the  numerous  easterly  dips  are 
interpreted  as  indicating  a  compressed  fold,  inclined  westward,  between  the  central 
syncline  and  the  eastern  one.  Between  East  mountain  and  the  central  Greylock  ridge, 
in  the  western  part  of  the  section,  minor  undulations  yield  alternating  areas  of  schist 
and  limestone  as  on  Section  M.  Both  this  and  the  following  section  indicate  an 
increasing  compression,  the  folds  becoming  more  numerous,  relatively  to  the  distance, 
less  open  and  more  inclined  than  on  Section  L. 

Section  0,  PI.  xxii,  starting  from  Cheshire  reservoir,  crosses  the  Farnham's 
quarry  limestone  area.     At  the  east  foot  of  the  high  schist  ridge,  which  presents  its 

precipitous  side  to  the  Hoosic  valley  (compare  PI.  xv 
with  this  section),  the  limestone  evidently  dips  under 
the  schist.  At  the  south  end  and  east  side  of  this  ridge 
the  schist  has  a  high  westerly  cleavage,  and  very  low 
westerly  or  horizontal  plications  (localities  315, 427, 325J), 
together  with  a  northerly  pitch  (locality  325).  Toward 
the  limestone  on  the  west  the  westerly  dip  ajipears  still 
^     ,„    „.     ,  ,.,      ^,      to  continue  (localities  325,410,411).    The  structure  at 

Fig.  70. — Structure  in  schist  ou  the  ^  77/ 

ridge  west  of  Cheshire  reservoir.  locality  315  is  represented  approximately  in  Fig.  70 ;  that 

at  locality  325  in  Fig.  .59,  p.  156. 

From  the  syncline  north  of  the  Farnham's  quarry  limestone  area  (Section  N),  from 
the  northerly  pitch  south  of  it  on  Savage  mountain,  from  the  westerly  dip  in  the 
schist  east  of  that  area,  and  the  easterly  dip  of  the  same  rock  west  of  it  (Section  O), 
from  the  character  of  the  dips  in  the  limestone  itself,  as  well  as  from  the  isolation  of 
this  limestone  from  that  of  the  Hoosic  valley,  it  has  been  inferred  that  a  schist  syn- 
cline underlies  the  Farnham's  quarry  limestone,  and,  therefore,  that,  although  litho- 
logically  identical  with  the  lower  limestone,  it  belongs  stratigraphically  with  the  up- 
per. We  have  here,  apparently,  asmall  limestone  basin  similar  in  structure  and  position 
to  the  larger  one  which  surrounds  and  underlies  Ragged  mountain.  The  difference  in 
the  limestone  of  these  two  areas  is  mainly  in  degree  of  metamorphism.  But  in  several 
places  the  limestone  of  Hoosic  valley  resembles  that  of  the  Notch.  About  half  a  mile 
SSW  of  the  west  end  of  this  section  (O),  at  the  east  foot  of  East  mountain  (locality  749, 
back  of  Mr.  Pine's  house),  the  schist  apparently  dips  east,  as  does  also  the  lime 
stone.  No  plications  are  discernible.  If  this  be  the  correct  dip  it  indicates  an  over- 
turn, the  dips  corresponding  to  those  on  the  east  side  of  Potter  m'ountain  (locality 
984)  and  on  the  road  from  Pittslield  to  Lebanon  (locality  1020). 


Cleavage  dip  15°w. 


MOUNT  GREY LOCK. 


175 


General  pitch  of  the  folds. — The  observations  of  pitch  are  recorded  on 
the  map  by  a  special  symbol.  It  will  be  noticed  that  the  direction  of  the 
pitch  through  the  northern  part  of  the  central  ridge  is  south,  while  at  its 
southern  extremity,  west  of  Cheshire  reservoir,  it  is  north.  Sugarloaf 
mountain,  New  Ashford,  has  a  northerly  pitch  at  its  south  end,  and  a  south- 
erly pitch  at  its  north  end.  Ragged  mountain  has  a  southerly  pitch  at  its 
north  end,  and  the  succession  of  the  horizons  at  the  surface  and  other  facts 
indicate  a  northerly  pitch  at  its  south  end.  From  the  "Bellowspipe"  the 
pitch  is  probably  both  north  and  south.  In  places  a  similar  pitch  seems  to 
prevail  along  parallel  lines  across  the  central  ridge  as  well  as  the  subordi- 
nate folds;  thus  the  southerly  pitches  on  the  Bald  mountain  spur,  the  north- 
erly pitches  on  Potter  mountain.  Constitution  hill,  and  the  Noppet,  and 
on  Savage  mountain  in  Lanesboro;  again,  the  northerly  pitch  at  Cheshire 
Harbor  is  xuidoubtedly  repeated  at  Round  rocks,  although  not  observed  there 
in  the  plications. 

LONGITUDINAL    SECTIONS. 

The  facts  stated  above  are  shown  on  the  four  longitudinal  sections 
appearing  on  PI.  xxiii.  Three  of  these,  on  a  reduced  scale,  are  given  in 
Fig.  71.     The  north  is  at  the  right. 


Fig.  71.— Longitudinal  .sections  P,  Q,  R. 

Section  P  follows  for  12  miles  the  axis  of  the  eastern  or  Rag-gred 
mountain  S5mcline,  beginning  at  the  Hoosic  river  a  little  south  of  North 
Adams,  between  Cross-sections  A  and  B.  At  the  north  end  of  Ragged 
mountain  the  upper  limestone  and  the  upper  schist  horizons  are  shown 
with  the  steep  southerly  jjitch  which  marks  the  whole  northern  end  of  the 
Greylock  mass  (compare  the  symbols  on  the  map).  On  Cross-section  F 
there  is  a  thinning  of  the  lower  schist.     There   are  some  indications  of  a 


176  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

northerly  pitch  on  the  east  flank  of  Ragged  mountain  west  of  Rowland's, 
between  Sections  F  and  E ;  but  along  the  Notch  brook  the  pitch  is  south 
like  that  on  the  Central  crest  (Section  Q).  The  deeper  part  of  the  syn- 
cline  is  about  under  the  center  of  Ragged  mountaiii.  Tlie  upper  lime- 
stone rises  to  the  surface  about  a  mile  soutli  of  the  south  end  of  this  moun- 
tain with  a  gentle  northerly  pitch,  ^  and  about  IJ  miles  farther  south  the 
underlying  schists  also  rise  to  the  surface,  forming  the  pinnacle  and  the 
neighboring'  schist  masses  which  hedge  in  on  the  south  the  northern  area 
of  the  upper  limestone.  South  of  this  is  the  Farnham's  quarrj'  limestone 
area,  with  well  observed  opposite  pitches  north  and  south  of  it,  forming-  a 
shorter  and  shallower  troug-h  in  the  same  axis.  The  section  ends  on  the 
east  of  Savage  mountain.  The  length  of  tlie  Ragged  mountain  trough  is 
about  Zi  miles,  and  the  entii-e  length  of  the  Farnham's  quarry  trough, 
extending  beyond  the  limit  of  the  section,  would  be  about  6  miles 

Section  Q  follows  for  14i  miles  the  axis  of  the  central  or  Clreylock 
syncline,  begimaing  at  the  foot  of  Clarksburg  mountain,  a  little  north  of 
Cross-section  A.  From  observations  made  hj  other  members  of  this  di- 
vision the  quartzite  of  Clarksburg  mountain  is  known  to  have  a  southerly 
pitch.  The  lower  limestone  is,  for  topogiviphic  reasons,  supposed  to  pass 
completel}^  around  between  the  Clarksljurg  and  Greylock  masses,  and  thus, 
of  course,  to  conform  in  pitch  to  the  horizons  below  and  above  it.  A  steep 
southerly  pitch  is  observed  at  the  north  end  of  the  central  crest,  Mount 
Williams.  This  section  shows  a  deep  trough  corresponding  to  that  on  Sec- 
tion P,  but  with  its  center  about  2  miles  farther  soutli,  at  Cross-section  I,  in 
the  saddle  between  Greylock  and  Saddle  Ball.  The  south  end  or  edge  of 
this  trough  is  at  Round  rocks,  almost  in  a  line  with  the  south  end  of  the 
great  trough  in  the  eastern  syncline.  This  trough  is  a  little  longer,  meas- 
uring 8J  miles.  In  the  incision  between  Round  rocks  and  Saddle  Ball  the 
upper  limestone   and  calcareous  schists  come  to  the  surface.     South  of  this 

'  North  of  thi.s  part  of  the  syncline,  at  the  south  end  of  Ragged  mountain,  tlie  vertical  distance 
between  the  top  of  the  upper  limestone  horizon,  where  it  is  overlaid  hy  the  smaller  mass  of  the 
upper  schist,  and  the  lowest  contour,  where  the  upper  limestone  occurs,  together  with  the  slight 
thickness  of  the  deposit  necessitate  a  southerly  pitch.  Thus  also  south  of  the  saddle  (the  Bellows- 
pipe)  ;  and  for  similar  reasons  a  northerly  jjitch  is  supposed  between  that  saddle  (Section  G)  and  lo- 
cality 632  in  the  Notch  (Section  F). 


MOUNT  GREYLOCK.  177 

is  a  shallower  trough  analogous  aud  parallel  to  the  minor  one  shown  oii 
Section  P. 

Sections  B'  and  JR"  pass  through  two  of  the  minor  synclines  on  the  west 
flank  of  the  Grreylock  mass;  R'  through  Stone  hill  and  Deer  hill,  the  syn- 
clinal axis  of  which  probably  continues  southward  through  East  mountain 
(Section  L)  and  Potter  mountain.  At  the  north  end  (see  Appendix  A,  Stone 
hill)  the  north  pitch  is  not  directly  observable,  but  is  pai'tially  indicated  by 
an  observation  of  Mr.  Hobbs  in  one  of  the  ravines  of  the  Taconic  range. 
The  relations  between  Stone  and  Deer  hills  are  a  repetition  of  those  which 
have  been  inferred  between  Clarksburg  mountain  and  the  Greylock  mass, 
the  quartzite  of  Stone  hill  pitching  under  the  limestone  of  Green  river,  and 
that  under  the  schists  of  Deer  hill. 

Section  B"  passes  through  Sugarloaf  mountain  (see  Appendix  B),  one 
of  the  smaller  lateral  synclinal  axes,  which,  farther  north,  appear  in  Bald 
mountain  and  Symond's  peak.  (Sections  G  and  I).  In  this  part  of  the  syn- 
cline,  which  .measures  only  about  6  miles  in  length,  there  are  two  well 
marked  troughs,  one  underlying  Sugarloaf,  and  the  other  the  high  schist 
ridge  south  of  it. 

RESUME,    STRUCTURAL. 

Mount  Greylock,  with  its  subordinate  ridges,  is  a  synclinorium  consisting 
in  its  broadest  portion,  of  ten  or  eleven  synclines  alternating  with  as  many 
anticlines.  While  the  nu  nber  of  these  minor  synclines  is  so  considerable  at 
the  surface,  it  is  found,  in  carrying  the  sections  downwards,  that  they  resolve 
themselves  chiefly  into  two  gi'eat  synclines  with  several  lateral  and  smaller 
ones.  The  larger  of  these  two  forms  the  central  ridge  of  the  mass ;  the  smaller 
one,  east  of  it,  forms  Ragged  mountain  and  an  inner  line  of  foothills  farther 
south.  The  anticline  between  these  coincides  with  the  Bellowspipe;  that 
on  the  west  of  the  central  syncline  is  a  little  west  of  the  north  and  south 
part  of  the  Hopper.  The  major  central  syncline  is  so  compressed  east  of 
Syinonds  peak  (Mount  Prospect)  and  Bald  mountain,  and  its  axial  plane  is 
so  inclined  to  the  east  that  the  calcareous  strata,  which  underlie  the  cen- 
tral ridge,  have  on  its  west  side  a  westeiV  dijj  (Sections  G  and  I).  Far- 
ther south  this  syncline  opens  out  (Section  K),  and  all  tlie  relations  become 

moi-e  normal.     But  between  the  villages  oi  Cheshire  nnd  Lanesboro  the 
MON  xxui 13 


178 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


folds  become  sharper    again  and   more  compressed,  and   the   schist  area 
rapidly  narrows  (Sections  N  and  O),  and  the  structure  continues  much  com- 

f^  pressed  to  the  extremity  of  the 
mass.     On  either  side  of  these 

p 

two  main  synclines  the  subordi- 

c  nate  folds  are  more  or  less  open, 
and  have  their  axial  planes  ver- 
tical or  else  inclined  east  or  west. 
The  continuity  of  the  folds  and 

^  their  nuitual  relations  are  shown 
in  Fig.  72.  Longitudinal  sec- 
tions along  the  two  main  syncli- 
nal axes  (P  and  Q )  show  that  the 
trough  bottom  deepens  at  two 
points.     In  the  eastern  syncline 

H  (P)  the  deeper  part  of  the  north- 
ern trough  is  shown  to  be  about 
under    the    center    of    Ragfo-ed 

'  mountain,  while  in  the  central 
one  (Q)  it  is  about  2  miles  far- 

,  ther  south  between  Grevlock 
and  Saddle  Ball  (Section  I); 
and  this  also  would  seem  to  be 

1/ 

the  deepest  part  of  the  entire 
.  synclinorium.  The  northern 
edge  of  both  of  these  troughs  is 
-  M  at  the  exti'eme  north  end  of  the 
N  Grevlock  mass,  and  their  south- 
Q  eru  edge  7^  to  8i  miles  distant, 
near  Round  rocks  and  the  soiith- 
east  spur  of  Saddle  Ball.  South- 
of  these  main  troughs  are  two 
shallower  parallel  ones,  the  centers  of  which  lie  west  of  Cheshire  reservoir 
(P,  Q).    To  the  west  of  these  two  long  axes  the  mountain  mass  is  made  up  of 


Flc.  72.— Diagram  showing  the  continuity  of  the  main  folds  in 
the  Grcyhick  synelinoriiun.     Keducetl  from  the  large  sections, 

Pis.  XVHI-XXII. 


MOUNT  GREYLOCK.  179 

numerous  minor  folds  which  do  not  show  the  continuity  seen  in  P  and  Q.  It 
will  be  observed  that  the  direction  of  these  two  main  synclines  represented 
by  P  and  Q  is  north-northeast  to  south-southwest,  thus  nearly  parallel  with 
the  direction  of  the  valley  lying  between  the  Clarksburg-  granitoid  mass 
and  Hoosac  mountain,  and  that  at  the  south  end  they  converge,  and  perhaps 
unite  in  the  narrow  schist  ridge  between  Berkshire  and  Lanesboro  vil- 
lages. Traversing  the  folds  of  this  canoe-like  complex  synclinorium  is  a 
cleavage-foliation,  sometimes  microscopically  minute,  dipping  almost  uni- 
formly east.  This  cleavage-foliation  is  distinct  from  the  "slaty-cleavage" 
early  described  by  Sedgwick,  Sharpe,  and  Sorby  and  reproduced  experi- 
mentally by  Tyndall  and  Jannetaz,  but  consists  sometimes  of  a  minute, 
abrupt,  joint-like  fracturing  of  the  stratification  laminae,  but  more  gener- 
ally of  a  faulting  of  these  laminae  as  the  result  of  their  extreme  plication — a 
mode  of  cleavage  "Ausweichungsclivage"  (slip  cleavage)  so  well  described 
by  Heim  and  recently  reproduced  in  part  by  CadelP  by  a  slight  modification 
of  the  experiments  made  by  Pi'of.  Alphonse  Favre,  of  Geneva,  in  1878.^  This 
fault-cleavage,  when  carried  to  its  extreme,  results  in  a  form  of  cleavage 
very  nearly  approaching,  although  not  identical  with,  slaty-cleavage.  To 
the  unaided  eye  all  traces  of  stratification-foliation  are  lost,  and  even  under 
the  microscope  they  are  so  nearly  lost  as  to  be  of  no  avail  in  determining 
the  dip. 


LITHOLOGIC   STRATIGRAPHY. 

As  may  be  inferred  from  the  descriptions  of  the  sections,  there  are  five 
more  or  less  clearly  defined  horizons  in  the  Glreylock  mass.  These  are 
described  below,  beginning  with  the  lowest. 

The  Vermont  formation.— T\\Q  iQ[(\B\)&\\\\(i  quartzite  of  the  northwest  end 
of  Deer  hill,  which  corresponds  to  the  quartzite  of  Clarksburg  and  Hoosac 
mountains  and  of  Stone  hill,  will  be  noticed  more  particularly  in  Appendix 
A,  on  Stone  hill.  This  is  Emmons's  "Granular  Quartz,"  and  has  recently 
been  shown  to  be  of  Lower  Cambrian  age. 

The  Stockbridge  limestone.^The  crystalline  limestone  of  the  Hoosac  and 
Green  river  valleys,  which  has  long  been  known  to  constitute  the  base  of 
Mount  Greylock,  is  the  Stockbridge  limestone  of  Emmons,  and  extends 

'  Op.  cit.  (see  p.  137),  third  series  of  experiments. 

» Alphonse  Fnvre ;   The  foruiatiou  of  uioiintains.    Nature,  \ol.  19,  1878,  p,  103, 


180  GKEEN  MOUNTAINS  IN  MASSACHUSETTS. 

tlii'ough  Berkshire  up  into  Vermont.     It  has  been  shown  to  be  of  Cambro- 
Sihirian  age. 

The  Berkshire  schist. — An  overlying-  mass  of  schist  forms  the  lower, 
steeper  slopes  of  the  mountains  on  all  sides.  This  is  a  part  of  the  magne- 
sian  or  talcose  slate  of  Emmons,  Dana's  hydro-mica  schist,  and  has  come 
to  be  regarded  as  of  Lower  Silurian  ag-e. 

The  BeUowspipe  Umestone. — A  series  of  limestone  strata  and  calcareous 
(sometimes  noncalcareous)  schists  constitutes  the  higher  benches,  the  Notch, 
and  the  Farnham's  Quarry  area.  In  places  the  rock  is  quartzite.  This 
horizon  seems  to  have  been  overlooked  by  previous  geologists  on  Greylock. 
In  1888  Mount  Everett,  near  Sheffield,  in  southern  Berkshire  county;  Mount 
,  Anthony,  near  Bennington,  Vermont;  Mount  Equinox,  near  Manchester, 
Vermont,  and  Mount  Dorset  (Eolus),  near  Dorset,  Vermont,  were  visited  by 
the  wriier  in  the  hope  of  finding  again  on  some  of  these  higher  summits  of 
the  Taconic  range  the  upper  limestone  and  calcareous  schist  of  Greylock, 
but  a  careful  exploration  of  them  all  failed  to  yield  any  trace  of  this  horizon, 
excepting  on  Mount  Anthony.  A  bench  of  calcareous  schist  occurs  there 
in  the  mass  of  schist  above  the  limestone,  but  the  relations  are  not  suf- 
ficiently clear  to  enable  one  to  determine  whether  these  calcareous  layers 
form  part  of  the  Berkshire  schist  or  Bellowspipe  limestone  formations.  Dur- 
ing the  year  1889,  however,  quartzites  were  found  on  Monument  mountain, 
in  southern  Berkshii'e,  which  appear  to  overlie  the  Berkshire  schist,  and 
thus  seem  to  belong  to  the  Bellowspipe  limestone  formation.^ 

The  Grei/Iock  schist. — A  second  series  of  schists  similar  to  the  lower 
ones  constitutes  all  the  higher  summits  of  the  central  ridge  and  the 
top  of  Ragged  mountain.  This  forms  part  of  Emmons's  magnesian  or 
Talcose  slate  and,  together  with  the  Berkshire  schist,  has  been  regarded  by 
Hall  and  Walcott  as  of  Hudson  River  age,  and  by  Dana  as  representing 
some  member  of  the  Lower  Silurian. 

All  these  groups  of  strata  succeed  each  other  conformably. 

•  The  theory  aflvanced  by  Mr.  W.  H.  Hobbs  duriug  the  printing  of  this  monograph  (see  Journal 
of  Geology,  vol  1,  Xo.  7,  Chicago,  October-November,  1893,  p.  72.T),  that  the  limestone  along  the  east- 
ern foot  of  Mount  Everett  corresponds  to  the  Bellowspipe  limestone  and  the  schists  which  overlie  it 
to  the  Greylock  schist  recjuires  verificeitiott  to  accord  -with  lesults  farther  north. 


MOUNT  GREYLOCK.  181 

PETROGRAPHY. 

The  petrographic  character  of  the  beds  of  these  formations  will  now  be 
described  with  tlie  aid  of  Mr.  J.  E.  Wolff's  notes  on  the  microscopic  sections, 
which  have  been  briefly  summarized. 

XnE    VEUMONT  I'OUMATION. 

As  the  beds  of  this  formation  are  only  represented  by  one  or  two  out- 
crops in  the  Grreylock  area  they  will  only  be  described  in  connection  with 
Stone  hill  in  Appendix  A. 

tHK   STOCKBRIDGE   LIMESTONE. 

The  lower  limestone  is  a  coarsely  or  finely  crystalline  limestone  or  mar- 
ble, usually  white,  but  often  banded  or  mottled,  and  in  places  entirely  dark 
grey,  and  there  argillaceous.  South  of  and  near  the  South  Adams  quar- 
ries it  is  very  quartzose,  and  at  the  south  end  of  Stone  hill  there  are  grad- 
ual passages  from  limestone  to  quartzite,  the  rock  consisting  of  an  "aggre- 
gate of  calcite  grains  with  rarely  a  small  grain  of  feldspar  and  of  quartz." 
About  Williamstown  and  along  the  Grreen  river  north  of  Sweet's  corners,  the 
limestone  is  very  fme  grained,  and  has  a  hardness  intermediate  between 
that  of  quartzite  and  limestone,  and  contains  occasional  quartz  grains. 
This  fine-grained  quartzose  limestone  may  be  more  characteristic  of  the 
base  of  the  horizon,  but  pure  quartzite  occurs  near  the  top. 

The  coarse  crystalline  limestone  is  often  so  micaceous  as  to  resemble  a 
gneiss.^  A  specimen  from  a  point  a  little  southeast  of  the  North  Adams 
reservoir  was  found  to  consist  of  "coarse  grains  of  calcite  interbanded  with 
muscovite  and  biotite,  and  containing  occasional  porphyritic  crystals  of 
feldspar.  The  feldspars  contain  inclusions  of  muscovite,  rutile,  pyrite,  etc. 
There  are  occasional  grains  of  quartz.  Some  fragments  of  feldspar  are 
microcline,  and  the  calcite  cuts  across  these  grains,"  indicating  the  possibility 
of  replacement  by  calcite.  The  limestone  about  Sugarloaf  mountain  is  also 
quite  micaceous.  Prof  Dewey  speaks  of  the  flexibility  of  this  micaceous 
limestone  from  New  Ashford.^  Lenses  and  seams  of  quartz  are  not  infre- 
quent.    Prof.  Emmons  noticed  the  occurrence  of  albite  in  the  limestone  of 

'  See  E.  Hitchcock.     Final  Report  Geology  of  Massachusetts,  p.  569. 

^  "Notice  of  the  flexible  or  elastic  marble  of  Berkshire  county."     Am.  .Jour.  .Sci.,  1st  ser.,  vol.  9, 
1825,  p.  241. 


182  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

Williamstown,^  also  the  presence  of  galena  and  zinc  blende  here  and  there 
in  small  quantities. 

Prof.  E.  Hitchcock  gave  five  analyses  of  the  limestone  of  this  horizon, 
which  show  it  to  be  in  places  a  dolomite.^ 

In  the  upper  part,  near  the  overlying  schist,  occur  iiregulai"  deposits 
of  limonite,  as  at  Cheshire,  and  along  the  north  side  of  Mount  Prospect, 
and  on  the  east  side  of  Potter  mountain.^  Prof  Dana  has  fully  explained 
the  origin  of  these  ii-ou-ore  beds.* 

Towards  the  upper  part  of  the  limestone  occur  also  sti-ata  of  quartzite; 
thus  on  the  east  side  of  the  extreme  end  of  the  Greylock  schist  mass  near 
Pittsfield,  and  also  near  the  Adams  quan-ies. 

The  fossils  foimd  by  Mr.  Walcott,  and  ah-eady  referred  to,  came  from 
this  horizon,  but  fossils  seem  to  be  exceedingly  rare.^ 

The  structural  peculiarities  of  the  rock  are  its  almost  universal  flexure 
into  minor  pitching  folds,  and,  as  already  explained  (p.  157),  its  not  infrequent 
mini;te  plications,  and  also  its  cleavage  sometimes  obliterating  all  ti-ace  of 
stratification. 

THE  BERKSHIRE   SCHIST. 

This  consists  of  the  lower  sericite-schists.  The  groundmass  of  these 
schists  is  made  up  of  interlacing  fibers  of  muscovite  (sericite)   and  folia 

'  Geology  Second  District,  New  York,  1842,  p.  158. 

^Fiual  Report  Geology  of  Massachusetts,  1841,  p.  80,  81. 

'At  tlie  latter  place  (Lanesboro  Iron  company's  ore  bed)  the  ore  occurs  in  two  positions.  In  one 
place,  owing  to  an  overturn,  it  lies  below  the  limestone  and  above  the  schist.  In  another  it  lies  on 
the  npper  side  of  a  small  limestone  anticline,  the  schist  capping  having  been  eroded.  In  another 
place  a  reddish,  partially  decomposed  schist  overlies  the  limestone,  the  ore  probably  occurring 
between.  The  stratigraphic  position  of  the  ore  is  identical  in  all  these  cases,  however.  On  the 
Rchist  side  of  the  ore  there  is  usually  a  mass  of  mottled  clay,  probably  originating  in  the  decomposi- 
tion of  the  schist,  and  on  the  limestone  side  a  yellowish  ochre.  Manganese  ore  (pyrolusite)  occurs 
here  associated  with  the  iron  ore  (limonite). 

^  Am.  Jour.  Sci.,  3d  ser.,  vol.  L4,  1877,  p.  132. 

Berkshire  geology  in  ''Four  papers  of  the  Berkshire  Historical  and  Scientific  Society,''  published 
by  the  society,  Pittsfield,  June  1,  1886,  p.  19. 

Much  of  interest  in  reference  to  these  Silurian  limonites  will  be  found  also  in  vol.  15  of  the 
Tenth  Census  (1880),  Washington,  1886,  especially  in  the  introductory  chapter  by  Prof.  Raphael 
Pumpelly  on  the  geographical  and  geological  distribution  of  the  iron  ores  of  the  United  States  (p.  10, 
on  the  limonites),  aud  also  in  Mr.  Bayard  T.  Putnam's  notes  on  the  samples  of  iron  ore  collected  in 
Connecticut  and  Massachusetts,  p,  87. 

■■•Since  the  completion  of  the  manuscript  the  writer  has  found  crinoid  stems  in  the  upper  part  of 
the  limestone  on  Quarry  hiU,  New  Ashford. 


MOUNT  GKEYLOCg.  l83 

of  chlorite  and  grains  of  quartz.  Whether  the  hydrous  character  of  the 
rock  proceeds  from  the  chlorite  or  from  some  other  hydrous  mica  can 
hardly  be  determined,  as  the  two  minerals  are  intimately  interlaced.  The 
talcose  appearance  and  touch  of  much  of  the  Greylock  schist,  which 
have  given  it  the  names  of  talcoid-schist,  hydro-mica  schist,  magnesian  slate, 
is  due  largely  to  the  presence,  almost  if  not  quite  universal,  of  these  exceed- 
ingly minute  folia  of  chloi'ite;^  and  the  variable  proportions  of  the  chlorite 
and  the  muscovite  in  different  localities  explain  the  difference  in  the  chem- 
ical analyses  of  it  as  well  as  the  variety  of  names  geologists  have  given  it. 
The  color  of  these  schists  varies  with  the  varying  proportions  of  its  prin- 
cipal ingredients — muscovite,  chlorite,  and  quartz.  Often  it  is  black  from 
the  presence  of  graphite,  or  porphyritic  from  the  presence  of  feldspar,  or 
spangled  from  the  presence  of  other  minerals.  Quartz  lenses  and  seams  are 
almost  universal.  There  are  also  great  variations  in  the  texture  of  these 
rocks.  Their  structural  peculiarities  have  been  described  at  length  on 
pages  138-157,  and  constitute  one  of  their  chief  characteristics 

The  following  is  a  brief  summary  of  Mr.  Wolff's  microscopic  analy- 
ses of  the  typical  specimens  collected :  Among  the  minerals  of  most  fre- 
quent occurrence  are  black  tabular  rhomboidal  crystals  or  lenticular  plates 
of  ilmenite  and  chlorite,  a  plate  of  ilmenite  being  interleaved  between  two 
of  chlorite.  "Similar  forms  have  been  described  by  Renard  from  the  met- 
amorphic  rocks  of  the  Ardennes,  but  they  are  surrounded  by  sericite  layers 
and  not  by  those  of  chlorite."  He  also  describes  large  plates  of  chlorite 
inclosing  small  octahedra  of  magnetite,  which  also  occur  on  Greylock.^ 
Very  minute  bluish  green  crystals  resembling  the  ottrelite  of  the  Rhode 
Island  Coal-measui'es  are  found.' 

Perhaps  fully  as  common,  if  not  more  so,  is  albite,  which  occurs  in 
simple  twins  or  untwinned,  sometimes  with  a  rim  of  clear  feldspar  separated 
or  not  from  the  central  crystal  by  a  rim  of  quartz,  and  surrounded  by 
fibers  of  muscovite  and  chlorite.     (Thus  specimens  from  locality  458,  south 

'See  E.  Hitchcock,  Report  Geol.  of  Vermont,  1861,  vol.  1,  p.  501.  James  U.  Dana,  Am.  .Jour. 
Sci.,  3d  ser.,  vol.  4,  p.  366,  and  vol.  14,  p.  139. 

"  See  A.  Renard,  Recherches  siir  la  composition  et  la  structare  des  phyllades  ardennais.  Bulletin 
Mus.  Roy.  Belg.,  vol.  2,  1883,  p.  127-152,  and  vol.  3,  1885,  p.  230-268. 

'See  .J.  E.  Wolff:  Ou  some  occurrences  of  ottrelite  and  ilmenite  schist  in  New  England.  Bull.  Mus. 
Comp.  Zool.,  Geological  Series,  vol.  2,  p.  159,  1890.    Cambridge,  Mass. 


184  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

of  Sugarloaf  mountain;  494,  between  that  mountain  and  Round  rocks; 
324,  on  the  line  of  contact  between  the  Stockbridge  hmestone  and  the  small 
mass  of  the  Berkshire  schist  south  of  Sugarloaf;  474,  in  the  deep  cut 
between  east  and  Potter  mountains ;  475,  at  the  southwest  end  and  foot  of 
East  mountain  in  Hancock;  and  703,  at  the  triangulation  point  on  the  north 
summit  of  East  mountain. 

More  rarely  garnets  occur,  giving  rising  to  chlorite.  Thus  at  locality 
40,  on  the  tongue  of  schist  north  of  the  Adams  quarries.  Garnets  occur 
also  in  the  small  isolated  schist  mass  west  of  Lanesboro  village. 

The  graphitic  schist  of  this  horizon  was  early  noticed  by  Emmons^  and 
Hitchcock.'^  It  generally  occurs  near  the  underlying  limestone,  as  about 
New  Ashford,  at  locality  274,  and  near  Maple  Grove  station,^ locality  139, 
on  the  east  side  of  Greylock.  The  graphite  is  in  microscopic,  irregular 
layers,  or  in  masses,  surrounded  by  even  sized  quartz  grains  and  scales  of 
gi-aphite  and  muscovite. 

Octahedral  crystals  of  magnetite  are  in  many  places  scattered  through 
the  schist,^  but  the  most  characteristic  minerals  are  albite,  interleaved 
ilmenite  and  chlorite,  and  graphite. 

The  rock  is  sometimes  calcareous,  but  not  continuously  so.  Rarely 
veins  of  calcite  and  chlorite  traverse  it.  Between  New  Ashford  and  Lanes- 
boro a  graphitic  limestone  occurs  in  the  schist,  containing  angular,  often 
rhombohedral,  crystals  of  albite  partially  replaced  by  calcite. 

THE   BELLOWSPIPE   LIMESTONE. 

For  structural  reasons  the  Farnham's  quarry  limestone  has  been  placed 
here.  That  limestone  is  generally  white  (though  sometimes  gray)  and  highly 
crystalline,  like  the  Stockbridge  limestone;  but  in  the  other  areas  of  this 
formation  the  limestone  is  finer  grained,  less  often  white,  frequently  argilla- 
ceous,  micaceous,  or  pyi'itiferous.  Frequently  the  micaceous  element  pre- 
dominates and  the  rock  is  a  calcareous  schist,  and  in  several  localities  the  cal- 
careous element  disappears  altogether.  Galena,  zinc  blende,  and  siderite 
occur  along  with  pyrite  in  the  limestone  of  the  Bellowspipe.  Associated 
with  these  limestone  and  calcareous  schists  are  beds  of  slightly  micaceous 

'  Geology  of  Second  District,  New  York,  p.  153. 

'  Final  Report  on  the  Geology  of  Massachusetts,  p.  581. 

'Emmons,  Geol.  Second  District,  New  York,  p.  141. 


MOUNT  GKBYLOCK.  185 

graiiulite  or  fine  grained  gneiss,  lliese  do  not  seem  to  be  confined  to  any- 
particular  portion  of  the  horizon,  nor  are  they  persistent  where  they  do  occur. 

The  seams  and  lenses  of  quartz  in  the  calcareous  schist  are  calcareous, 
and  the  rock  itself  is  often  calcareous  where  it  looks  least  so,  and  vice  versa. 
In  structure  it  shows  the  same  peculiarities  as  the  limestone  and  schist  of 
the  lower  horizons. 

No  fossils  have  yet  been  found  in  this  formation  on  Greylock,  although 
the  rock  in  many  places  is  sufficiently  fine  grained  and  not  too  metamor- 
phic  for  their  preservation. 

The  only  reason  for  the  entire  omission  of  this  horizon  from  Emmons's 
section  seems  to  be  that  his  section  traversed  the  mountain  in  one  of  the  few 
places  where  there  are  no  outcrops  on  the  calcareous  belts.^ 

The  following  is  a  summary  of  Mr.  Wolff's  report  on  these  rocks.  A 
bluish  gray,  finely  crystalline  limestone  composed  of  calcite  grains  and 
quartz  grains,  with  occasional  flakes  of  muscovite  and  considerable  pyrite 
scattered  tlu"ough  the  calcite.^  (Thus  a  specimen  from  locality  212  on  Peck's 
brook,  about  2  miles  south  of  the  Bellowspipe.)  Traversing  the  limestone 
are  thin  beds  of  graphitic,  pyritiferous  quartzite  composed  of  quartz,  feldspar, 
pyrite,  graphite,  and  muscovite.  (Thus  locality  704  in  the  Notch  about 
three-quarters  of  a  mile  south  of  its  highest  point.) 

The  calcareous  schist  is  composed  of  large  grains  of  calcite  mixed 
with  stringers  of  muscovite  and  graphite  containing  inclusions  of  mica, 
graphite,  calcite,  and  quartz.  Pyrite  and  small  fragments  of  microcline  also 
occur  in  it.  (Thus  a  specimen  from  locality  712  on  the  west  side  of  Ragged 
mountain  near  its  south  end.) 

The  feldspathic  quartzite  so  often  associated  with  or  replacing  the  cal- 
careous schist  of  this  horizon  consists  of  an  interlocking  aggregate  of  grains 
of  qviartz  and  feldspar  with  rare  flakes  of  muscovite,  small  crystals  of  rutile, 
and  specks  of  limonite  (thus  at  locality  345  in  the  Notch,  west  of  the  center 
of  Ragged  mountain);  and  the  gneiss,  which  seems  intimately  related  to  the 
above,  is  a  mixture  of  quartz  with  a  large  amount  of  feldspar,  twinned  and 
untwinned  j)lagioclase,  with  occasional  grains  of  microcline  and  muscovite 

'  See  Emmons's  American  Geology,  part  2,p.  18.  "  From  the  termination  of  the  limestone  [i.e.,  the 
Stockbriilge  limestone]  to  the  top  of  Greylock  the  talcoso  slate  is  uninterrupted." 

^Recent  assays  of  a  similar  specimen  of  this  horizon  are  said  to  have  shown  the  pyrite  to  be  aurif- 
erous, but  not  sufficiently  so  to  give  the  rock  any  metallurgical  value. 


186  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

plates,  magnetite,  zircon,  rutile,  etc.     (Thus  at  locality  616,  in  the  gneiss 
area  west  of  King  Cole  mountain  and  Maple  Grove  station.) 

THE   GREYLOCK   SCHIST. 

This  also  consists  of  schists  resembling  in  their  petrographic  character, 
appearance,  and  structure  those  of  the  Berkshire  schist  formation.  If  there 
be  any  difference  between  them  it  consists  in  that  the  upper  schists  are 
more  chloritic  and  albitic,  and  less  frequently  calcareous  or  plumbaginous 
than  the  lower  ones,  but  all  the  minerals  occux-ring  in  the  Berkshire  schist 
recur  in  the  Greylock  schist. 

The  interleaved  plates  of  ilmenite  and  chlorite  are  the  same  as  in 
the  Berkshire  schist.  (Thus  specimens  from  locality  1,076  in  the  most 
southerly  of  the  Hopper  ravines,  about  1,300  feet  below  Grreylock  summit.) 

The  magnetite  octahedra  are  also  frequently  met.  (Thus  at  locality 
449  in  the  cliffs  on  the  south  side  of  Saddle  Ball,  and  again  west  of  the 
top  of  Grey  lock  about  a  quarter  of  a  mile  east  of  locality  1,076.) 

The  feldspathic  schists  of  this  formation  are  characterized  here  and 
there  by  large  crystals  of  albite.  At  locality  709,  on  the  west  side  of  the 
Notch,  east  of  Mount  Fitch  near  section  F,  the  rock  might  be  called  an 
albite-gneiss.  It  consists  of  "numerous  squarish  albite  crystals,  rarely  in 
simple  twins,  crowded  closely  together,"  but  surrounded  by  "interlacing 
fibers  of  muscovite,  chlorite,  and  biotite  with  magnetite  grains  and  many 
tourmaline  needles.  Quartz  occurs  rarely,  in  little  grains  or  aggregates. 
The  biotite  and  chlorite  are  often  in  separate  masses,  but  often  pass  into 
one  another  in  the  same  piece.  Some  of  the  chlorite  may  result  from  the 
hydration  of  biotite.  The  feldspars  contain  inclusions  of  muscovite,  chlo- 
rite, biotite,  magnetite,  tourmaline,  etc."  Mr.  Wolff  separated  the  feldspar 
of  this  rock  by  the  use  of  the  Thoulet  solution,  and  a  double  analysis  of  it 
was  made  at  the  chemical  laboratory  of  the  U.  S.  Geological  Survey  in 
Washington  by  Mr.  R.  B.  Riggs  (F.  W.  Clarke,  chief  chemist).  The  result 
shows  the  feldspar  to  be  an  almost  pure  albite. 


MOUNT  GREYLOCK. 

Analysis  No.  567.     Feldspar  from  specimen  709a,  D.  I.     1886, 


187 


SiO, 

Al,03+(Fe.03<5%) 

MnO 

CaO 

MgO 

Na^O 

KjO 

Ignition 


I. 

II. 

68.08 

67.83 

20.11 

19.92 

trace 

trace 

trace 

trace 

? 

? 

11.00 

11.65 

.36 

.25 

.31 

.12 

99.86 

99.77 

Dried  at  105  C.     Sliecific  gravity  slightly  above  2. 6545,  between  2.  6.545  ami  2.  fil.' 

At  the  south  eiid  of  the  top  of  Ragged  mountain  in  the  small  isolated 
schist  area  (locality  764),  the  albite  gneiss  is  "coarsely  foliated  with  a 
wavy  sti'ucture  composed  of  bands  of  dark  mica,  alternating  with  irregular 
layers  of  calcite  mixed  with  quartz  and  large  rounded  feldspar  crystals. 
Needles  of  tourmaline  occur  occasionally.  The  albite  crystals  are  not 
twinned,  have  a  rounded  outline,  often  lie  with  their  longer  axes  across  the 
foliation  of  the  rock,  and  contain  inclusions  of  calcite,  quartz  grains,  and 
flakes  of  both  micas.  The  groundmass  consists  of  interlacing  fibrous 
layers  of  muscovite  and  biotite,  little  grains  of  quartz  and  great  quantities 
of  calcite,  not  in  grains  but  in  masses.  The  calcite  sometimes  penetrates  a 
large  feldspar,  breaking  it  up  into  isolated  cores  of  feldspar,  surrounded  by 
calcite.  It  is  difficult  to  say  with  certainty  whether  the  calcite  was  formed 
later  than  the  quartz  and  mica  or  contemporaneously  with  them.  It  occurs 
in  vein-like  masses,  not  in  grains ;  when  it  has  encroached  on  the  feldspar 
it  does  so  irregularly  and  not  parallel  to  the  schistosity  of  the  rock,  as  the 
quartz  and  mica  do;  rarely  tongues  of  calcite  cut  in  two  inclusions  of 
quartz  in  the  feldspars — it  seems  rather  therefore  to  be  pseudomorphous — 
replacing  quartz  as  well  as  feldspar." 

Towards  the  top  of  Greylock  and  along  the  central  ridge  the  feldspar 
crystals  are  very  minute  and  are  not  rounded.  (Thus  at  locality  861  on 
the  Greylock  road.) 

'  Mr.  Wolfi'  adds  for  comparison  the  analysis  of  a  colorless  all)ite  from  Kiriibinsk,  Urals.     SiOj 
68.45,  AljOa  18.71,  FeO  0.27,  NaOi!  11.24,  K^O  0.6.5,  CaO  0.50,  MgO  0.18.      Total  100.      Spec.  grav.  2.624. 


188 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


Fig.  73  represents  a  slightly  enlarged  section  of  a  specimen  of  the  felds- 
pathic  schists,  which  may  be  regarded  as  petrographically  and  structurally 
typical  of  this  formation. 

From  all  the  foregoing  the  transitional  lithologic  character  of  the  for- 
mations is  manifest.'  In  the  Stockbridge  limestone  there  are  passages  from 
limestone  to  qiiartzite  and  to  schist.  In  the  Berkshire  schist  the  rock 
is  often  calcareous.  In  the  Bellowspipe  limestone  there  are  transitions 
from  limestone  to  calcareous  schist,  and  from  these  to  noucalcareous 
schists  and  to  quartzite  and  gneiss.  Mr.  AVolff's  microscopic  examinations 
indicate  that  this  feature  is  due  in  part  to  vainous  replacements  and  other 


Fig.  73.— Thin  section  of  albitic  seritite-schist  fiom  locality  542,  between  Greylock  summit  ami  SadiUe  Ball, 
enlarged  IJ  diameters.  A  typical  specimen  of  the  Greylock  schist,  showins  the  minute  plications,  the  (|uart7,  lamina?, 
the  slip  cleavage  with  the  alhite  interspersed.     {From  a  jihotograph.) 

chemical  changes  at  the  time  of  or  subsequent  to  metaraorphi.sm,  as  well  as 
in  part  to  variations  in  tlie  character  of  the  original  sediments. 


THICKNESS-. 


The  numerous  folds,  and  the  fact  that  they  are  sometimes  compressed 
and  overturned,  not  to  mention  the  difficulties  arising  from  cleavage,  render 
exact  measurements  of  thickness  very  difficult,  if  not  impossible,  in  the 
Greylock  area,  but  approximations  can  be  obtained.  The  figures  appended 
to  the  following  table  are  given  only  as  estimates  based  upon  the  sections. 
The  difference  in  the  estimates  arises  in  pai-t  fi-om  the  varying  amount  of 
thickening  in  plication  (Stauung).     As  thickening  in  consequence  of  plica- 

'  Prof.  J    D-  Daua  refers  to  this  in  several  of  his  papers  on  the  Taconic  rocks. 


MOUNT  GREYLOCK.  189 

tion  g-enerally  occurs  in  the  Greylock  mass  the  actual  tliickuess  is  probably 
less  than  the  minimum  figures  given  in  the  table,  and  may  possibly  be 
considerably  less.  It  will  be  observed,  however,  that  the  maximum  thick- 
ness of  the  entire  series  does  not  exceed  the  minimum  thickness  attributed 
to  the  Lower  Silurian  rocks  in  the  Appalachian  region.^ 

GEOLOGIC   AGE. 

The  question  of  the  age  of  the  beds  of  Gfreylock,  and  the  treatment  of 
the  whole  subject  from  the  standpoint  of  historic  geology  are  beyond  the 
province  of  this  report,  but  the  various  conclusions  which  have  been  reached 
and  are  being  reached  in  regard  to  the  geologic  age  of  these  formations  are 
added  in  separate  columns  for  convenience  of  reference. 


'  See  J.  D.  Uana,  Manual  of  Geology,  third  edition,  jiji.  Itt2,  210. 


190 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


KESUME,    LITHOLOGIC    STRATIGRAPHY. 

The  (jentrul  lilholugic  character,  order,  and  estimated  thickness  of  the  strata  of  Mount  Greylock,  East 

mountain,  and  Stone  Mil. 


Formatious, 
natural  order. 

/ 

Age.' 

Lithologic  character. 

Thickness. 

Emmons,  1855. 

Hall, 

1839-1844. 

Dana, 

1882-1887. 

Walcott, 

1888. 

Feet 

Greylock 

Muscovite  (aericite),  chlorite,  and 

1,500-2,200 

Pre-Potsdam. 

Trenton. 

Lower  Si- 

Trenton. 

schist. 

quartz  schist,  with  or  without  bi- 

Lower   Taconic 

(Hudson 

lurian. 

(Hudson 

Sg- 

otite,    albite,  magnetite,  tabular 
crystals  or    lenticular   plates  of 
interleaved  llmenite  and  cldurite. 
ottrelite,    inicroscopic  rutile  and 
tourmaline. 
Tliese  schists  are  rarely  calcareous 
or  graphitic. 

No.  3.     "Talcose 
or   magnesian 
slate." 

river.) 

river.) 

Bel  1 0  w  s  ]>  i  p  ti 

Linieatone,  more  or  less  crystalline, 

600-700 

Pre-Potsdam, 

Trenton. 

Lower  Si- 

Trenton. 

liiuestone. 

generally  micaceous  or  pyritifer- 

LowerTaconic 

(Hudson 

lurian. 

(Hudson 

Sbp. 

ous,  pnssing  into  a  calcareous 
schist,   or  a  feldspathic  quartz- 
ite,  or  a  fine-grained  gneiss  with 
zircon  and  microcline,  or  a  schist 
like  Sb. 
The  more  common   minerals  are: 
Graphite,  pyrite,  albite,  and  mi- 
croscopic rutile  and  tourmaline. 
More  rare:  Galena,  zinc   blende, 

No. 3.  Included  in 
"Talcose  or  mag- 
nesian slate." 

river.) 

river.) 

siderite. 

i 

Berkshiro 

Muscovite  (sericite),  chlorite,  and 

1,000-2,000 

Pre-Potadam. 

Teenton. 

Lower  Si- 

Trenton. 

schist. 

quartz  schist,    with  or  without 

Lower   Taconic 

(Hudson 

lurian. 

(Hudson 

Sb. 

biotite,  albite,  graphite,  magne- 
tite;   frequently   with    tabular 
crystals  or  lenticular  jdates  of  in- 
terleaved  ilmenite  and  chlorite. 
Garnet,  ottrelite.   Microscopic  ru- 
tile and  tourmaline. 
These    schists    are    in    places  cal- 
careous,   especially   towards   the 
underlying  limestone,  where  they 

No.  3.     "Talcose 
or   magnesian 
slate." 

river.) 

river.) 

are  often  graphitic. 

Stockbridge 

Limestone,  crystalline,  coarse  or 

1,200-1,400 

Pre-Potsdam. 

Lower  Si- 

Lower Si- 

Trenton. 

limestone. 

tine;  in  places  a  dolomite,  some- 

Lower   Taconic 

lurian. 

lurian. 

(Trenton.) 

ess. 

times  quart zose,  or  micaceous, 

No.  2.    "Stock- 

(Trenton 

Canadian. 

more  rarely  feldspathic,  very  rare- 

bridge lime- 
stone.^ 

and  lower.) 

(Chazv, 

ly  foasiliferous.     Galena  and  zinc 

Califer- 

blende  rare.     Irregular  masses  of 

ous.) 

iron  ore  (limonite)    associated 

sometimes  with  siderite,  often 

with  manganese  ore  (pyrolusite). 

Some  quartzite. 

Vermont   for- 

Quartzite, fine  grained,  alternating 

800-900 

Pie-Potsdam. 

Cambrian. 

Lower 

mation. 

with    a  thin- bedded,    micaceous, 

Lower    Taconic 

(Potsdam.) 

Cambrian. 

ev. 

and  feldspatbic  quartzite.     (The 
latter  with  calcite,  pyrite,  tour- 
maline.)    Associated  with  these 
quartzites,   and  probably  at  the 
base  of  this  horizim.  is  a  coarse- 
grained micaceous  quartzite  (tour- 
maline) passing,  in  places,  into  a 

No.  1.    "Granu- 
lar quartz." 

(Olenel- 
las.) 

cony:lomerate.   and   containing 

blue  quartz,  feldspar  (plagioclase, 

microcline)  and  zircon,  all  of 

clastic  origin. 

Total  thickness: 

Minimum 

5,000 
7,200 

Maximum 

'  For  Prof.  E.  Emmons's  views  see  his  works  already  referred  to,  especially  his  American  Geology,  Part  2,  pp.  10-18, 
48,  128. 

For  Prof.  James  Hall's  views,  announced  as  early  as  1839-1844,  but  not  then  published,  see  American  Journal  of 
Science.  3d  ser.,  vol.  28,  October,  1884.  p.  311 :  "  Prof.  James  Hall  on  the  Hudson  river  age  of  the  Taconic  slates."  Also 
Jules  Maroon :  "On  two  plates  of  stratigraphical  sections  of  Taconic  ranges  by  Prof.  James  Hall,"  Science,  vol.  7,  1886, 
p.  393.  New  York. 

For  Prof.  Dana's  views  see  his  papers:  "  (xeological  Age  of  the  Taconic  System,"  Quarterly  Journal  of  the  Geolog- 
ical Sociely  of  L(mdon,  vol.  38,  188"J.  p.  3'.)7 ;  "On  Taconic  Rocks  and  Stratigraphy,"  American  Journal  of  Science.  3d  ser., 
vol.  33,  May,  1887,  p.  410.  and  also    'On  the  Hudson  river  Age  of  the  Taconic  Sc-hists,"  etc.,  ibid,  vol  17,  1879.  p.  375. 

For  Mr.  diaries  D.  Walcott's  views  see  the  map  and  section  appended  to  bis  paper,  "  The  Taconic  system  of  Emmons, 
and  the  use  uf  the  name  Taconic  in  geologic  nomenclature,"  American  Journal  of  Science.  3fl  ser.,  vol.  25.  April,  Ma.y, 
1888,  pp.  307,  394,  pi.  3,  also  "The  Stratigraphicai  auccessioa  of  the  Cambrian  Faunas  iii  North  America"  (abstract  of  hie 


MOUNT  GREYLOCK.  191 

AREAL   AND    STRUCTURAL. 

The  geologic  map  of  the  Greylock,  East  and  Potter  mountain  masses, 
presents  a  great  body  of"  the  schists  of  the  Berkshire  schist  formation,  sur- 
rounded by  the  underlying  Stockbridge  limestone.  It  is  probable,  although 
not  demonstrable,  that  this  limestone  passes  around  the  north  end  of  the 
Greylock  mass,  between  the  schist  on  the  south  and  the  quartzite  (Vermont 
formation)  of  Clarksburg  mountain  on  the  north.  It  is  also  probable  that 
that  quartzite  underlies  the  entire  Greylock  synclinorium,  for  it  occurs  on 
the  north  on  Clarksburg-  mountain,  on  the  east  on  Hoosac  mountain,  and 
on  the  west  on  Stone  liill,  and  is  also  brought  up  again  by  a  fault  on  the 
east  side  of  Deer  hill. 

The  Bei'kshire  schist  sends  out  tongues  corresponding  structurally  to 
syuclines  into  the  lower  limestone  area,  as  west  of  Zylonite  on  the  east  side 
of  the  range,  and  at  Deer  hill  on  the  west  side ;  also  at  Constitution  hill, 
west  of  Lanesboro.  There  are  also  reentering  angles  of  limestone  in  the 
schist  area,  corresponding  to  anticlines,  as  nortli  of  Lanesboro,  and  about 
New  Ashford. 

There  are  isolated  schist  areas,  generally  lenticular  in  form,  corre- 
sponding to  more  or  less  open  synclines,  as  a  little  southwest  of  South 
Adams,  and  south  of  Constitution  hill,  in  Lanesboro  and  about  New  Ash- 
ford. The  most  interesting  of  these  is  Sugarloaf  mountain,  which  is  a 
canoe-shaped  open  syncline.  (See  Fig.  74,  Appendix  B,  and  Sections 
M,  R.") 

There  are  also  isolated  limestone  areas,  corresponding  to  compressed 
anticlines,  projecting  through  the  overlying  schists,  exposed  by  their  erosion. 
Two  of  these  occur  between  New  Ashford  and  Lanesboro,  and  a  smaller 
one  is  described   in  Appendix  B,    at  Quarry  hill,   New  Ashford.     (Figs. 

remarks  before  tho  lutornational  Geological  Cougress.  Lourtou,  September,  1888).  in  Natiu'e,  vol.  38,  No.  23,  October  4, 
1888,  p.  .551;  also  Ills  paper,  "Straligrapbic  Position  of  tbe  Olenellus  Fauna  in  North  America  and  Europe,"  American 
Journal  of  Science.  3(1  ser.,  vol.  37.  May,  1889,  p.  374. 

For  a  defense  of  Emiuou.s's  classilicatiou  see  "Pal:i?ontologic  and  Stratigraphic  Principles  of  tbe  adversaries  of  the 
Taconic,"  by  Jules  Marcou,  American  Geologist,  July,  1888;  and  for  Mr.  Marcou's  own  classification  of  the  Taconic 
rocks  see  his  memoir,  "The  Taconic  system  and  its  position  in  stratigraphic  geology,"'  Proceedings  of  tho  American 
Academy  of  Arts  and  Sciences,  vol.  12.     Cambridge,  ISi^-S,  p.  174. 

For  a  summary  of  the  dilfercnt  phases  of  opinion  in  regard  to  the  age  of  the  Taconic  rocks  see  "A  brief  history  of 
Taconic  itleas,"'  by  J.  D.  Dana,  Am.  Jour.  Sci.,  3d  ser.,  vol,  36.  December,  1888,  p.  40. 

For  tbe  literature  and  a  8y.=demati<-.  presentation  of  the  Taconic  question  .lee  Bulletin  81,  U.  S.  Geol.  Survey,  Correla- 
tion Papers — Cambrian,  by  Chas".  D.  Walcott.  For  evidence  of  the  Loweri  Cambrian  age  of  the  lower  part  of  the  Stockbridge 
limestone,  see  article  by  J.  E.  Welti",  "'  On  tlje  Lower  Cambrian  age  of  the  Stockbridgelimestone,"  Bull.  Geol.  Soc.  Am.,  vol. 
2,  1890,  p.  331.  Also  paper  by  T.  Nelson  Dale,  "  On  the  structure  and  age  of  the  btookbridge  limestone  in  the  "Vermont 
Talley,''Bull.  Geol,  Soc.  Am.,  vol.  3,  1891,  p.  514, 


192  GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 

78,  79.)     The  limestone  area  iu  the   western  part  of  the  Bald  mountain 
spur  is  anticlinal  in  structure,  but  faulted. 

The  relations  which  have  been  described  above  as  existing  between 
the  lower  limestone  (Stockbridge  limestone)  and  the  lower  schist  (Berk- 
shire schist)  are  repeated  at  a  higher  level  between  the  upper  limestone 
(Bellowspipe  limestone)  and  the  upper  schist  (Greylock  schist).  Ragged 
mountain  and  the  higher  portions  of  the  central  ridge  (Saddle  Ball,  Grey- 
lock,  Fitch,  Williams)  are  synclinoria  of  the  upper  schist  resting  upon  and 
surrounded  by  the  upper  limestone.  The  tongues  and  reentering  angles  and 
isolated  schist  areas  occur  here,  as  well  as  in  the  lower  formations.  But  the 
isolated  limestone  area  southwest  of  Cheshire,  instead  of  being  an  anticline 
of  the  Stockbridge  limestone  projecting  through  the  Berkshire  schist,  seems 
to  be  a  syncline  of  the  Bellowspipe  limestone  resting  upon  the  Berkshire 
schist,  homologous  to  that  which  encircles  and  underlies  Ragged  mountain, 
but  without  any  similar  mass  of  schist  on  it.  The  relative  height  of  the 
surface  of  the  Farnham's  quarry  limestone,  as  shown  in  Section  P,  accords 
well  with  this  interpretation.^ 

RELATIONS  OF  GEOLOGY  TO  TOPOGRAPHY. 

It  remains  now  to  show  the  relations  of  the  structural,  lithologic,  and 
areal  geology  to  the  surface  features.  We  fhid  here  evidence  of  the  opera- 
tion of  several  causes : 

First.  The  mineralogic  character  of  the  rock,  presenting  minerals  more 
or  less  easily  disintegrated  by  physical  or  chemical  agencies. 

Second.  The  internal  structure  and  position  of  the  strata,  forming  ele- 
vations and  depressions  in  the  mass  and  determining  the  surface  relations 
of  the  different  kinds  of  rocks. 

Third.  Erosion,  glacial,  as  well  as  pre-glacial  and  post-glacial,  bringing 
physical  and  chemical  agencies  to  bear  upon  those  irregularities  in  the  form 
and  composition  of  the  surface. 

'  These  facts  are  brought  out  on  the  accompanying  map  and  the  sections  (Pis.  i,  xvm-xxili). 
Besides  the  usual  dip  and  strike  symbols  there  have  been  added  on  the  map  symbols  indicating  the 
direction  and  angle  of  jiitch,  and  also  the  symbols  proposed  by  Dr.  H.  Reusch  (op.  cit.)  to  indicate 
the  cleavage  dip  and  strike,  aud  IJually,  uumbers  of  the  important  localities  referred  to  in  ttis 
report. 


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USGEOLOSICAL  SURVEY 


MONOGRAPH  XXIII  PL  XVIII 


MT.  nnKYLOCK 

\'crli(;tl  .'MIorizDiilril  Scale  linnri  orli  iiichcs-l  mil  p. 

SYMBOLS- 
CHLOR-MICA  ISERICITCISCHIST_ 

CALCAREOUS  MICA-SCHIST  &  LIMESTONE 

ifi placesllieScl'fstisnorCalcareous.in ptacesQuartrite    _  _ 

LIMESTONE  _   _ 

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MONOGRAPH  XXllI  PL  XX 


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U.  8.  GEOLOGICAL  SUHVEY 


V  SotXifmsf  tjUurt "/"/ 


M^^GREYLOCK 

Longitudinal  Sections. 


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MOUNT  GEEYLOOK.  193 

The  interaction  of  all  these  have  molded  the  mountain  and  given  it 
its  varied  topography. 

The  phj^sically  and  chemically  more  resistant  schists  form  the  more 
elevated  portions;  also  the  steeper  and  more  rugged  and  wDoded  slopes,  while 
the  broad,  cultivated  valleys  of  the  Hoosic,  Green,  and  Housatonic  rivers, 
and  the  more  gently  undulating  portions  of  the  mountain  generally  correspond 
to  limestone  areas.  The  upper  limestone  strata  and  calcareous  schists  con- 
stitute the  benches  of  agricultural  and  pasture  land,  which  form  so  marked  a 
feature  in  the  Greylock  landscape,  and  to  which  attention  was  directed  in  the 
Introduction.  Thus  the  Notch  and  the  agricultural  character  of  its  surface 
find  their  explanation  partly  in  its  anticlinal  structure  and  partly  in  the  cal- 
careous element  of  its  strata.  The  character  of  the  bench  on  the  east  flank 
of  Ragged  mountain  has  already  been  noticed.  Similarly  the  broad  bench, 
which  extends  for  2  miles  at  an  altitude  of  2,000  to  2,500  feet  above  sea 
level  on  the  west  side  of  the  central  ridge  between  Gt-reylock  and  Saddle 
Ball  and  around  "Jones's  Nose"  (see  Pis.  xiii,  xiv),  corresponds  to  the 
gently  inclined  strata  of  Formation  Sbp,  witli  its  easily  weathering  and 
subsoil-forming  micaceous  limestone.  This  accounts  for  the  farms  which 
once  dotted  its  surface,  still  mostly  recognizable  as  open  pasture  land. 
Thus,  also,  is  explained  the  incision  between  Round  rocks  and  Saddle  Ball. 
(Fig.  74  and  Section  Q.) 

The  2^-mile  long  north  to  south  extension  of  the  great  Hopper  cut  was 
partly  occasioned  by  the  trend  of  the  folds  and  partly  by  the  upturned  edges 
of  the  calcareous  belt,  which,  on  the  north,  at  "Wilbur's  pasture,"  and,  on 
the  south,  at  "Shattuck's  flats,"  still  retain  something  of  their  former  surface 
outline.  (See  PI.  xvii.)  Prof  Dana's  surmise  that  the  north  to  south  Hopper 
depression  is  due  to  a  subordinate  anticline^  is  correct,  but  the  anticline  seems 
to  occur  on  the  west  side  of  the  Hopper.  The  main  east  to  west  Hopper 
incision  does  not  seem  to  correspond  to  any  structural  featm-e,  but  to  be 
simply  the  result  of  the  surface  drainage  of  the  west  slope  of  the  range  eating- 
back,  i.  e.,  eastward,  through  the  subordinate  folds  until  it  reached  the  cal- 
careous belt,  and  then,  owing  possibly  in  part  to  the  sharpness  and  conse- 
quent weakness  of  the  anticline  west  of  it,  but  mainly  to  the  more  assailable 

f 

1  On  the  quartzite,  limestone,  etc.,  in  the  vicinity  of  Great  Barrington,  Massachusetts,  p.  273. 
MON  XXIII 13 


194 


GREEN  MOUNTAINS  IN  MASSACHUSETTS. 


character  of  the  calcareous  belt,  and  its  general  trend,  erosion  proceeded 
quite  as  rapidly  laterally,  north  and  south,  along  the  strike  as  easterly  across  it. 
The  deep  incisions  south  of  the  Bald  mountain  spur  (Goodell  brook, 
Mitchell  brook,  etc.).  and  the  corresponding  ravines  on  the  east  slope  of  the 
range  (Peck's  brook,  Bassett's  brook,  etc. )  are  the  usual  effects  of  the  drain- 
age of  a  mountain  range ;  and  the  alternation  of  precipice  and  gentle  declivity 
in  these  ravines  is  explained  by  differences  in  the  character  of  the  noncal- 
careous  schists  themselves,  and  also  by  the  alternation  of  calcareous  and 


Sadd/e  03//.     Jones'A/ose      NewAs/rfordCfy.  Rouncf  ffocks.      SugsrLoaf 
UpperSc/t/sf:       Ca/c.Schisf-  Lower  Sc/tisf 


s,';^' 


N. 


Fig.  74.— Outline  skftili  of  Rcmiirt  rocks  aud  the  northern  alope  of  Saddle  Ball  and  Sugarloaf  mountain  from  th- 
west,  locality  772  on  East  mountain,  ahowinp;  the  hollow  between  Round  rocks  and  Saddle  Ball  due  to  the  erosion  of  the 
calcareous  schist  (Bellowspipe  limestone) ;  also  the  cliff  at  Round  rocks  in  the  Berkshire  schist,  and  the  upper  bench  ou 
Saddle  Ball  in  the  Greylock  schist. 

noncalcareous  schists.  Some  (.)f  these  ravines  are  quite  as  steep  aud  diffi- 
cult of  access  as  any  in  the  Hopper. 

The  problematic  upi)er  bench  on  Saddle  Ball  (see  PI.  xiii,  Fig.  74  and 
Section  K)  is  possibly  due  in  part  to  the  horizontal  position  of  the  strata 
along  a  portion  of  the  slope,  aud  possibly  in  part  also  to  pre-glacial  erosion. 
These  benches  and  tliose  on  the  long  southeast  spur  of  the  same  mountain 
may  also  be  coimected  with  the  gentle  northerly  pitch  of  the  south  end  of 
the  great  troughs.     They  require  further  study. 

The  saddle  between  Greylock  summit  and  Saddle  Ball  seen  for  a  great 


MOUNT.  GREY  LOCK. 


195 


distance  south  (PI.  xv)  is  due  to  the  syndinal  structure  of  the  central  ridge, 
the  westerly  dip  onlhe  east  side  of  Grreylock,  the  easterly  dip  on  the  west 
side  of  Saddle  Ball.  The  saddle  in  the  central  crest  as  seen  from  Mount 
Equinox,  i.  e.,  the  north  northwest,  is  due  to  the  pitch  of  the  sides  of  the 
central  trough.  (See  Fig.  30  and  Section  Q.)  The  northeast  to  southwest 
trend  of  the  ridge  between  the  two  summits  and  the  northerly  trend  of  the 
central  ridge  north  of  Grreylock  correspond  to  changes  in  the  direction  of 
the  strike,  but  the  general  trend  of  East  mountain  does  not  conform  to  the 
strike  of  its  strata. 

The  two  depressions,  alternating  with  three  elevations,  seen  on  the  range 


Alt  Prospect-         BcddMt  ^ur 


•ScuUILp-  Ball. 


I~t/>iLn£L.fiac/ts 


Fig.  75.— Sketch  of  the  Greylock  m,iss  from  the  .southwest  (locality  1008,  on  north  Potter  mount.iiii)  showing  the  .surfiice 
of  the  Bald  nimmtain  spur  anil  of  Round  rock.s  pitching  toward  each  other  owing  to  the  pitch  of  the  .syurlinoi-ial  axis. 

from  Clarksburg  mountain  and  the  Stamford  valley  are  due  to  the  presence 
of  the  two  iDelts  of  the  upper  limestone  and  calcareous  schist  on  either  side 
of  the  central  ridge  (Berkshire  schist)  one  forming  the  Notch,  the  other 
"Wilbur's  pasture,"  and  the  north  to  south  part  of  the  Hopper. 

The  gentle  northerly  slope  of  the  surface  from  Hound  rocks  to  Jones's 
Nose  (see  Fig.  74,  and  Section  Q),  and  the  similar  southerly  slope  of  the 
top  of  the  Bald  mountain  spur,  as  seen  from  North  Potter  mountain  on  the 
southwest  (Fig.  75),  are  probably  due  to  the  trough  structure  of  the  entire 
mass,  the  former  constituting  a  part  of  the  northern  trough  of  the  great  cen- 
tral syncline.     To  this  structure  are  probably  also  due  the  long,  steep  south- 


196  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

ern  face  of  Round  rocks  and  the  steep  south  side  of  Saddle  Ball.  The  former 
is  a  very  striking  object  in  the  landscape  both  from  the  east  and  west. 
(Compare  Section  Q  with  PL  xiii  and  Fig.  74).  An  east  to  west  system  of 
joints  and  fractures  growing  out  of  the  pitch  may  have  aided  glacial  and 
other  erosion  at  these  points. 

The  great  west  spurs  which  characterize  the  west  side  of  the  range 
(PI.  xiii)  are  portions  of  the  mass  left  by  the  erosion  which  chiseled  out  the 
Hopper  and  the  hollows  farther  south,  while  the  pleasing  variety  of  surface 
features  seen  on  the  east  side  from  Hoosac  mountain  (PI.  xii)  is  the  result 
of  the  Berkshire  schist  forming  a  sei'ies  of  foothills  between  the  upper  and 
the  lower  limestone..  Some  of  these  are  also  shown  in  PI.  xv,  the  view 
from  Lenox  mountain.  East  of  the  summit,  however,  these  schists  have  been 
eroded  almost  down  to  the  level  of  the  Stockbridge  limestone,  thus  enabling 
one  to  look  over  from  Hoosac  mountain  into  the  area  of  the  Bellowspipe 
limestone  and  southwards  for  2  miles  to  a  point  where  the  Berkshire  schist 
rises  from  under  the  Bellowspipe  limestone  and  hedges  it  in  ("The  Canoe" 
PI.  xii),  forming  several  considerable  masses,  the  pinnacle  and  the  southeast 
spur  of  Bald  mountain.  These  constitute  the  ridge  between  the  northern 
and  the  southern  trough  of  the  eastern  syncline  and  shut  in  the  view.  (Com- 
pare PI.  XII  and  Section  P.) 

A  careful  comparison  of  the  topography  and  geology  of  the  map,  with 
the  transverse  and  longitudinal  sections,  and  the  general  views  (Pis.  xii, 
XIII,  XV,  and  Figs.  30,  75)  will  show  more  clearly  than  words  can  the  general 
structural  relations  of  the  Grreylock  mass  to  its  surface  features. 


APPENDIX    A. 

STONE  HILL,  NEAR  WILLIAMSTOWN. 

This  oft-studied  and  problematic  locality  has  not  yielded  anything  very  remark- 
able.' Observations  of  strike  and  dip  were  made,  typical  rock  specimens  were  col- 
lected and  submitted  to  Mr.  Wolff  for  microscopic  examination.  Three  cross  sections 
have  been  constructed,  S,  T,  U  (Fig.  76),  and  one  longitudinal  one,  E'  (PL  xxiii).  The 
dififlculties  at  Stone  hill  arise  from  the  small  number  of  outcrops  and  their  entire 
absence  at  critical  points. 

The  areal  geology  of  the  hill  is  indicated  on  the  geologic  map.  The  first  question 
which  arises  is  whether  the  mass  of  quartzite  along  the  east  side  of  West  brook  val- 
ley, apparently  overlying  the  .limestone,  forms  a  part  of  the  quartzite  at  the  top  of 
the  hill.  There  is  a  gentle  slope  of  arable  land  between  the  two,  and  a  small  lime- 
stone outcrop  on  the  east  side,  at  the  north  end  of  the  westerly  mass,  has  a  foliation 
which  strikes  with  the  trend  of  this  strip  of  cultivated  land.  It  has  therefore  been 
conjectured  that  the  two  masses  are  separated  by  limestone,  but  the  other  supposition 
would  be  tenable. 

The  dips  in  the  main  mass  of  quartzite,  on  both  sides  and  in  the  center,  are 
easterly;  but  at  the  south  end  the  dip  (pitch?)  is  south,  and  a  well  marked  southerly 
pitch  occurs  in  the  quartzose  limestone  at  the  southwest  end  of  the  hill  (localities 
1103-1105).  A  very  high  southerly  pitch  occurs  also  iu  the  limestone  a  little  farther 
south  (locality  62)  on  the  north  side  of  the  Green  river  bridge  crossed  by  the  road  from 
Sweefs  corners  to  South  Williamstown.  Here  there  is  a  small,  sharp  anticline  with 
an  almost  vertical  pitch.  A  southerly  pitch  occurs  again  iu  the  schists  at  the 
north  end  of  Deer  hill.  High  up  on  the  southeast  side  of  Stone  hill  (locality  1106) 
an  outcrop  of  quartzite  with  limestone  north  of  it  shows  a  southeast  pitch.  This, 
however,  has  been  regarded  as  a  quartzose  part  of  the  limestone.  Formation  €3Ss.  From 
all  these  facts  the  quartzite  at  the  top  of  the  south  end  of  Stone  hill  appears  to  pitch 
under  the  limestone  farther  south  and  down  the  hill,  and  that  limestone  to  i>itch 
under  the  Berkshire  schist  of  Deer  hill.  We  thus  have  here  in  their  normal  succes- 
sion, the  Vermont  formation,  the  Stockbridge  limestone,  and  the  Berkshire  schist, 
and  the  relations  which  seem  to  exist  between  Clarksburg  mountain  (Oak  hill)  and 
the  north  end  of  the  Greylock  mass  are  repeated  here  between  Stone  hill  and  Deer 

'  See  Emmons:  Geology  of  the  Second  District  of  New  York,  pp.  145,  156,  159;  Report  on  agricul- 
ture pp.  83-86.     James  D.  Dana:   Taconic  rocks  and  stratigraphy,  p.  406;  Geology  of  Vermont  and 

Berkshire,  p.  206. 

197 


198 


GEEEN  MOUNTAINS  IN  MASSACHUSETTS. 


bill.  (See  sections  Q  and  R')-  These  relations  at  the  south  end  of  the  hill,  together 
with  the  structure  of  Buxton  hill  and  the  northerly  pitch  observed  by  Mi-.  Hobbs  at 
locality  2005,  a  little  west  of  Buxton  hill,  lead  to  the  supposition  that  the  quartzite 
of  the  top  of  the  hill,  at  the  north  end,  pitches  under  the  limestone  at  Williamstowu. 
The  correctness  of  this  conclusion  is  also  rendered  probable  by  the  petrographic 
character  of  the  Stone  hill  beds,  which  is  similar  to  that  of  the  Oak  hill  beds.  On 
the  east  of  Stone  hill  strata  of  micaceous  feldspathic  quartzite  occur  between  those 
of  massive  quartzite  (locality  627).    In  three  localities  a  flue  schist  or  phyllite  of 


Observed 
Stratify  dips 


.  lOOOFl 

.  700 
.500 


TooLof  TaconicRanae  roaa 

l5'-2Q3tf  5S6OWMt,S0°     50" North  part  of  45°  Probable  Green 

E.El      E.prookE        E.  Stone  Mill     t.   Fault  R. 


_Sea  level 


Izl888 


660  Ffc 


Observed 
StratiFC  dips 

EioooFd. 
700 
500 
300 
Sea  level 


West 
Brpoh 


4d'S0°3Z42°65°    Probable 
roadEX.     f.    E-        Fault, 


-*-E 

Green 
R. 


•CSS.  700  Ft, 


Observed 
StratiFC  dips 


i 


ioooFl 


700 
500 


West 
Brook 

I 

I 


V  >E 

Stone  Hrll  75^55?60'  Green 

roao     South  part  LE.  PtDbatJieFault.  R 


720  Fb. 


•C55 

Sea  level  "df:'') 

Fig.  76.— Cross-sectious  S,  T,  U,  Stone  Hill. 

inconsiderable  thickness  appears.  Towards  the  north  end  of  the  east  side  of  the 
hill  a  blue  ijuartz  conglomerate,  and  a  quartzite  containing  blue  quartz  and  detrital 
feldspar  occur.'     Mr.  Wolff's  descriptions  of  these  rocks  are  given  beyond. 


'  Dewey :  "Granitell  of  Kirwan,  quartz,  and  feldspar.  This  aggregate  forms  extensive  strata  at 
the  east  base  of  Stone  hill,  the  feldspar  is  ditt'iised  in  grains  through  the  quartz,  and  sometimes  crys- 
talline, forming  porphyritic  fjuartz.  This  aggregate  is  often  compact  and  very  hard,  hut  frequently 
it  is  porous  and  hard,  forming  good  millstones.  Sometimes  the  quartz  appears  in  such  fragments 
that  the  stone  resembles  breccia."    Am.  Journal  of  Science,  ser.  i,  vol.  I,  1819,  p.  343. 

See  also  Emmons,  American  Geology,  p.  16,  on  the  conglomerate  of  the  granular  quartz  at  Oak  hill. 


STONE  HILL.  "  ]iJ9 

In  constructing  transverse  sections  of  Stone  hill  several  difficulties  present  them- 
selves. The  quartzite  with  detrital  blue  quartz  and  feldspar,  which  may  naturally 
be  supposed  to  occur  near  the  base  of  the  quartzite  and  towards  some  underlying 
gneissoid  rock,  and  which  Emmons  places  at  the  base  of  his  "granular  quartz," 
occurs  only  on  the  east  side  of  the  hill  dipping  toward  the  limestone  outcrops  of 
Green  river  and  Williainstovvn  (Formation  €!Ss).  On  the  west  side  of  the  western 
mass  of  quartzite  the  rock  is  massive,  and  seems  to  be  conformably  underlain  by  the 
limestone  of  Formation  €Ss,  but  that  quartzite  we  should  expect  to  reiiresent  the 
upper  part  of  the  quartzite  (Formation  €v). 

One  explanation  of  these  facts  would  be  that  on  the  west  the  apparent  superpo- 
sition of  the  quartzite  upou  the  limestone  is  the  result  of  an  overturn,  while  on  the 
east  the  two  rocks  are  separated,  as  Emmons  supposed,  by  a  fault.'  Such  a  fault 
would  be  nearly,  if  not  quite,  on  the  line  of  the  fault  on  the  east  side  of  Deer  hill  (Sec- 
tion G),  and  with  that  farther  south  near  the  west  end  of  the  Bald  mountain  spur 
(Section  I)  and  also  on  a  line  with  faults  in  southern  Vermont  at  East  Pownal.  The 
highly  contorted  character  of  the  limestone  strata  along  Green  river  east  of  Stone 
hill,  and  in  the  village  of  Williamstown^  also  leiul  probability  to  such  a  hypothesis. 

Upou  this  basis  of  fact  and  probability  the  folds  in  the  Stone  hill  sections  have 
been  constructed.  On  the  east  side  of  Stone  hill  a  fault  is  represented;  the  central 
portion  of  the  hill  consists  of  a  syncline  followed  on  tlie  west  by  an  anticline  over- 
turned to  the  west;  the  outlying  masses  of  quartzite  on  the  southeast  and  northwest 
sides  of  the  hill  involve  two  minor  anticlines.  All  the  folds  have  a  southerly  pitch  at 
the  south  end  of  the  hill  and  a  northerly  one  at  the  north  end. 

The  entire  thickness  of  the  Stone  hill  (juartzite  and  its  associated  micaceous  feld- 
spathic  rocks  would  thus  measure  between  800  and  900  feet.  If  a  simple  anticline  be 
supposed  it  would  measure  about  1,300  feet,  and  if  a  monocline,  as  represented  by 
E.  Hitchcock  in  his  Massachusetts  section,  about  2,600  feet.^ 

The  rocks  of  Stone  hill  are  frequently  jointed;  one  of  the  systems  of  joints  may 
possibly  be  connected  with  the  pitch,  as  may  also  the  occasional  east  to  west  joints 
and  some  of  the  secondary  cleavage  planes  on  Greylock.  On  the  east  side  of  the 
southern  portion  of  the  hill  the  massive  quartzite  is  traversed  by  joints  striking 
north  65°  east,  and  dipping  05°  to  75°  northwesterly.  On  the  east  side  of  the  central 
part  the  micaceous  quartzite  has  a  set  of  joints  striking  north  80^  east  and  dipi)ing 
80°  southerly,  and  another  set  striking  north  L'Oo  west,  and  dipping  45°  easterly.  The 
dark  pyritiferous  quartzite  (locality  18)  near  the  top  and  center  has  joints  striking 
north  72°  east,  and  dipjting  65°  north-northwest. 


'See  his  Section  46  (Geology  second  fUstriet,  New  York,  p.  145),  in  wUicli  lie  repi'csents  a  I'ault 
immediately  eiist  of  Stone  hill,  and  another  farther  east  along  the  western  foot  of  the  Greylock  range. 
^  Dewey  refers  to  the  contortions  here:  Am.  Jour,  of  Sci.,  ser.  i,  vol.  9,  1825,  p.  18. 
'  Report  Gaol,  of  Vermont,  vol.  2,  pi.  xv,  fig.  5. 


200  GREEN  MOUNTAINS  IN  MASSACHUSETTS. 

The  following  is  Mr.  J.  E.  Wolflf's  summary  of  his  notes  on  the  Stone  hill  micro- 
scopic sections: 

STONE   HILL   ROCKS. 

"We  have  in  the  quartzite  series  of  Stone  hill  an  interesting  illustration  of  the 
share  that  the  original  detritus  and  the  modification  produced  by  mechanical  and 
chemical  agencies  take  in  producing  certain  rocks. 

"The  quartzite  varies  microscopically  from  a  fine-grained  rock,  composed  to  the 
eye  of  quartz  grains  and  more  or  less  mica  to  a  coarse  fragmental  quartzite  or  fine- 
grained conglomerate  (locality  628)  in  which  angular  fragments  of  feldspar  and  rather 
rounded  masses  or  pebbles  of  blue  quartz  are  visible;  the  latter  grade  insensibly  into 
the  granular  white  quartz  forming  the  rest  of  the  rock. 

"Studied  in  the  thin  section  the  structure  of  the  rocks  is  as  follows:  The  large 
masses  of  blue  quartz  show  in  polarized  light  that  they  have  been  subjected  to  great 
pressiu'e  and  strain,  which  has  resulted  in  a  partial  or  total  breaking  up  of  the  original 
homogeneous  quartz  into  a  'groundmass'  or  mosaic  composed  of  extremely  small 
particles  of  quartz  in  which  are  contained  cores  of  cracked  and  strained  quartz  which 
are  remnants  of  the  original  masses.'  The  comparatively  large  fragments  of  feld- 
spar are  seen  to  be  in  most  cases  microcline  or  a  plagioclase  feldspar,  but  sometimes 
without  evidence  of  multiple  twinning,  and  in  that  case  probably  orthoclase.  The 
substance  of  the  feldspar  is  cloudy,  owing  to  kaolinization.  The  forms  are  sharj)ly 
angular  and  evidently  detrital.  The  remainder  of  the  rock  is  a  very  fine-grained  aggre- 
gate of  little  grains  of  quartz  and  rarer  ones  of  feldspar,  the  latter  being  similar  in 
character  to  the  larger  fragments  of  the  same  mineral.  Irregular  and  interrupted 
layers  of  a  colorless  muscovite,  which  has  the  wavy  'interwoven'  structural  form 
characteristic  of  sericite,  give  the  rock  a  lamination,  the  plane  of  which  is  parallel 
to  the  planes  of  crashing  in  the  quartz,  that  is,  at  right  angles  to  the  pressure.  When 
one  of  these  layers  of  mica  touches  one  of  the  large  clastic  feldspars,  it  often  forks  and 
completely  siu-rounds  the  feldspar,  the  two  parts  joining  again  on  the  other  side; 
accompanying  this  there  is  a  thickening  of  the  layer  of  mica  around  and  near  the  feld- 
spar, and  sometimes  litttle  tongues  of  the  mica,  branching  from  the  main  mass  outside, 
penetrate  the  feldspar,  especially  along  cleavage  cracks.  It  is  therefore  evident  that 
the  clastic  feldspar  exercised  an  influence  on  the  formation  of  the  mica  and  probably 
gave  up  part  of  its  substance  to  form  the  latter.  These  large  feldspars,  like  the 
quartz,  are  fractured  and  broken,  the  quartz  aggregate  of  the  'groundmass'  filling 
the  fissures. 

"The  small  feldspars  of  the  'groundmass'  have  in  part  the  same  characters  as 
the  large  detrital  ones,  and  in  fact  are  often  evidently  derived  from  an  adjacent  large 

'  See  PI.  X  in  Part  il  for  an  enlarged  photograph  of  a  thin  section  of  this  cruehed  blue  quartz 
from  Stone  hill.  > 


STONE  HILL.  201 

grain,  but  in  part  they  have  a  more  rounded  form  and  show  little  trace  of  decompo- 
sition. In  some  of  these  grains  there  is  a  central  core  which  is  opaque  owing  to 
kaolinization  (as  is  the  case  with  the  whole  grain  in  the  case  of  the  large  fragments) 
but  surrounded  by  an  outer  rim  of  clear  fresh  feldspar  material,  which  has  the  same 
crystallographic  orientation  as  the  inner  core,  the  two  forming  one  grain.  If  these 
grains  are  detrital,  as  they  seem  to  be,  there  must  have  been  a  recrystallization  of  the 
old  feldspar  or  a  deposition  of  new  feldspar  around  the  old  grain. ^ 

"In  certain  finegrained  varieties  of  these  Stone  hill  quartzites  the  amount  of 
feldspar  is  very  large,  and  it  is  difficult  to  say  whether  these  small  grains  are  in  their 
original  detrital  shape  or  are  metamorphic. 

"  In  sojae  cases  the  large  clastic  feldspar  masses  are  aggregates  of  several  individ- 
ual grains  of  feldspar,  forming  thus  a  rock  fragment  which  resembles  closely  the 
coarse  granitoid  gneiss  found  on  Clarksburg  mountain  to  the  northeast  and  Hoosac 
mountain  to  the  east,  which  undei'lies  the  whole  Taconic  series.  Hence  there  is  a  pos- 
sible derivation  for  the  material  of  the  quartzite. 

"  Prisms  of  tourmaline  are  common  in  the  rock,  and  there  are  occasional  rounded 
grains  of  zircon.  Secondary  limonite  often  stains  the  rock  yellow.  Grains  of  pyrite 
are  abundant  in  some  specimens  (locality  IS,  near  top  of  hill),  and  in  one  there  is  a 
large  amount  of  calcite  present  in  small  grains  and  irregular  masses. 

"These  quartzites  seem  to  derive  their  present  materials  from  two  sources,  the 
original  detrital  material  and  the  material  produced  from  this,  at  least  in  part,  by 
mechanical  and  chemical  agencies.  The  blue  quartz  'pebbles'  (locality 628, east  side) 
may  be  regarded  as  pebbles  whose  original  outlines  have  been  largely  obliterated  by 
mechanical  deformation ;  the  large  feldspar  fragments  are  undoubtedly  detrital  and 
so  is  the  zircon.  The  cement  or  'groundmass'  is  composed  of  detrital  quartz  and 
leldsijar  mixed  with  an  unknown  amount  of  the  same  minei-als  formed  in  situ  and  by 
muscovite  in  large  part  and  tourmaline  produced  by  metamorphism. 

"The  distinction  made  here  between  clastic  and  metamorphic  feldspar  is  well 
marked  in  the  extremes  as  found  on  the  clastic  side  in  these  rocks;  on  the  metamor- 
phic side  in  the  albite  of  the  schists  of  Greylock  and  Hoosac  mountains,  and  analo- 
gous feldspars  of  the  gneisses  of  Hoosac  mountain." 

'Cf.  Irving  and  Van  Hise,  Bull.  U.  S.  Geol.  Survey  No.  8,  p.  44. 


APPENDIX   B. 


NEW  ASHFORD. 


Fig.  77.— Apex  of  the  main  anticline  of  Stockbridge 
limestone  protruding  ttimugli  the  Berkshire  schist  at 
Quarry  hill,  New  A&hford.  Height,  6  feet.  Southern 
side.    See  locality  296,  Fig.  78. 


There  is  an  area  of  between  3  and  4  square  miles  south  and  east  of  the  village  of 
New  Ashford,  within  which  nearly  all  the  structural  and  areal  features  that  char- 
acterize the  Greylock  mass  are  repeated  on  a 
small  scale  and  within  easy  reach.  PI.  i  shows 
the  geology  of  this  tract.  Section  M  traverses 
it.  Fig.  74  gives  a  view  of  the  greater  portion 
of  it  and  of  Sugarloaf  mountain  which  covers 
a  large  part 'of  the  area.  This  little  schist 
mountain,  the  synclinal  struc';urD  of  which 
has  already  been  alluded  to,  is  entirely  sur- 
rounded as  well  as  underlain  by  limestone. 
It  forms  a  conspicuous  object  in  the  land- 
scape, views  of  it  from  the  north  (Fig.  30)  and 
the  south  (PL  xv)  showing  the  depression  on 
either  side  of  it  corresponding  to  the  limestone. 
A  line  of  cliffs,  masked,  however,  by  foliage,  traverses  its  south  end  from  east 
to  west,  rising  above  the  limestone  which  pitches  under  it.  On  the  west  side  of 
Sugarloaf  the  synclinal  structure  is  concealed  in  most  of 
the  limestone  out-cro]is  by  cleavage  foliation.  (See  Fig.  37.) 
A  northerly  pitch  is  well  observed  at  the  south  end  in  some 
of  the  minor  folds  (see  Fig.  60),  as  well  as  a  southerly  pitch 
in  the  schist  at  the  north  end.  Section  II",  which  follows 
the  synclinal  axis  of  Sugarloaf,  shows  the  trough  structure 
of  that  mountain.  Another  trough  exists  in  the  schist  mass 
south  of  it. 

Several  isolated    schist  masses   cap  the   limestone  folds 
along  the  foot  of  the  mountain  on  the  south.    The  phenomena 
of  cleavage  and  stratification  in  one  of  these  have  been  shown  in  Fig.  35. 

On  Quarry  hill  the  converse  of  the  structure  presented  by  Sugarloaf  mountain 
appears.    A  limestone  anticline  with  subordinate  folds  protrudes  through  the  schist. 
202     • 


Fig.    78 Geologic     map     of 

Quarry  hill.  New  Ashford. 


NEW  ASHFOUl). 


203 


The  diaigraiiis  (Figs.  77, 78,  7'.»)  leprcseut  the  area,  size,  and  structm-e  of  this  anticline, 
and  Figs.  32,  33,  3i  show  the  cleavage  phenomena  iu  it. 

The  schists  at  the  foot  of  the  hill  toward  the  village  form  part  of  those  of  East 
mountain  (Beach  hill).  The  easterly  cleavage  would  easily  mislead  oue  here  into  a 
wrong  interpretation  of  the  relations.    The  broad  area  of  limestone  in  which  the  old 


Ashford      Schisl     Sb  3S'S-£  SChtst       +5"  S  £        SchiStSb 

''■'""  r'  QUARRT    Hiltl 


:7"''12;^4s.s/i^^^;^!'!^i 


Fig.  70. — Section  through  Quarry  hill,  Xt;\v  Ashlbrrt,  showing  the  structural  relations  of  the  Stockbridge  limestone 
and  Berkshire  Hchist. 

quarries  lie,  forms  an  anticline,  and  the  schists  referred  to  overlie  its  base  with  a 
westerly  dip.  It  is  uncertain  whether  the  section  given  by  Emmons  (Geology  of  sec- 
ond district,  p.  155),  through  the  New  Ashford  marble  quarry,  relates  to  this  quarry 
or  to  one  of  several  others  iu  the  vicinity. 


INDEX 


Page. 

Adam9,Mas9.,  exposures  of  gneiss  near 84 

Ampbibolites,  areas  and  character  of 65-66 

Anthonys  creek,  exposures  on s4 

Ausweichungsclivage  of  Hoim 139 

Bald  mountain,  figured  specimen  of  schist  from.   ...  144 

Baltzer,  A.,  cited 143 

"Bellowspipe,"  location  of 160 

Bellowspipe  limestone,  thickness  of 20 

age  and  character  of 180, 184-186 

Berkshire  schist,  exposures  of 08 

syncline  of,  in  Cheshire 15, 16 

thickness  of 20 

age  and  character  of 179, 182-184 

Berkshire  valley  described 6 

Bowens  creek,  section  on 85 

Burlingames  hill,  exposures  at 85 

"  Buttress,"  location  and  structure  of 22 

exposures  of  gneiss  at 83 

Cadell,  H.  M.,  cited, 179 

Cambrian  quartzite  correlated  with  Hoosac  conglom- 
erate       28.29 

Cambrian  and  pre-Cambrian  rocks  not  easily  distin- 
guished    25 

Cambrian  rocks,  varying  character  of 31 

Cheshire,  schist  and  limestone  in 16 

ideal  section  near 17 

Cheshire  hills,  transition  from  limestone  to  schist  at 

south  end  of 16, 17 

Chester  ampbibolites,  geologic  place  of 30 

Clarksburg  mountain,  structure  of 8-9, 10,  27, 176 

rocks  of 26,27 

exposures  at 99 

Cleavage,  list  of  works  on 137, 138 

nature  of.  Mount  Greylock 158 

Cleavage  and  stratification  foliations,  relations  of. .  136-137, 
139, 140, 141, 144-155, 155-157, 161, 173 

Connecticut  valley  described 6 

Conway  schist,  place  of 30 

Cook,  George  H.,  cited 157 

Correlation  of  Green  mountain  rocks 9, 35 

Dale,  T.  Nelson,  work  of xiv,  12, 19-20 

paper  on  Mount  Greylock  by 119-203 

cited 191 

Dalton,  exposures  in 96 

Dalton-Windsor  hills,  structure  of 16 

Dana,  J.  D.,  cited 9, 50, 1 07, 

131, 132, 155, 157, 159, 163, 169, 182, 188, 189, 190, 193 

Darwin,  C,  cited 143 

Deer  hill,  location  of 135 

Dewey,  Chester,  cited 131 ,  163, 181, 198 

Dry  brook,  exposures  near 91, 93, 94, 96, 98 

East  mountain,  specimen  of  limestone  from 142 

figured  specimen  of  schist  from 146 

Eaton,  Amos,  cited 131 

Emerson,  B.  K.,  work  of 10, 26,  30 

Emmons,  B.,  cited  14, 1U7, 131, 

132, 159, 163, 164, 181,  184, 185, 190, 197. 198, 199 


Page. 

Favre,  A  Iphonse,  cited 179 

Feldspar,  analysis  of 187 

Formations,  table  of 190 

Geology  and  topography,  relations  of 192-196 

Greylock  schist,  thickness  of 20 

age  and  character  of 180,186 

Greylock  and  Hoosac  rocks  correlated 13-20 

Hall,  James,  cited 108,132,159,190 

Hawes,  G.  W.,  cited 67 

Heim,  A.,  cited 106,139 

Hitchcock,  C.  H  ,  cited 7,58,100,107 

Hitchcock,  E.,  cited 67,107,131, 

132, 159, 164, 181, 182, 183, 184, 199 

Hobbs,  W.  H.,  work  of xvi,  131 

aid  by 12 

cited 180 

Hoosac    conglomerate    correlated    with    Cambrian 

quartzite 28, 29 

Hoosac  mountain,  structure  of 8, 20, 21, 80, 104-106 

rocks  of 26,44-69,102 

report  of  J.  E.  Wolfi' on 35-118 

general  topography  of 41-44 

Hoosac  tunnel,  geologic  value  of -■ 8 

described 8.9,42,69-72 

Hoosac  schist,  exposures  of,  in  tunnel 23,69,72 

described 59 

exposures  of 72,80,81,82,87,88 

Hoosac  schist  and  Stockbridge  limestone,    zone  of 

lateral  transition  between 15, 17 

Hoosac  and  Greylock  rocks  correlated 13-20 

Hoosic  river,  exposures  on 87 

Hoosic  valley  schist  97-98 

*' Hopper,"  location  of 134 

Hunt,  T.  Sterry,  cited 108 

Irving  and  Van  Hise,  cited 201 

Jukes,  J.  B.,  cited 143 

Lachines  creek,  contact  of  Stockbridge  limestone 

and  Cambrian  quartzite  on 12 

Logan,  "W.  E.,  cited '. 7 

Marcou,  Jules,  cited 191 

Metamorphism,  phases  of 32, 33, 34 

Mount  Greylock,  structure  of 21, 125-127, 177-1 79 

structure  of  rocks  of 102, 127-128, 136-155, 181 

paper  by  T.  Nelson  Dale  on 119-203 

description  of 125,133-136 

areal  geology  of 128 

relations  of  geology  to  topography  on 128, 129 

figured  specimens  of  schist  from 145,147 

pitch  of  folds  of 175 

table  of  formation s  of 190 

Mount  Prospect  (Symonds  peak),  location  of 134,135 

figured  specimens  of  schist  from 144, 145 

structure  of 162-163 

New  Ashford,  geology  of  area  near 202-203 

North  Adams,  exposures  at 87-88, 98 

205 


20*) 


INDEX. 


"Notch,"  location  of 

( ileuelhis  casts  tniiml 

Pierce,  Josiali,  ;iid  by 

Pitili,  methoils  of  dtterioininji, 

general.  Mount  (Ireylock 

riaiiilieUl  schist,  geoloj;ic  phice  *if- 


Page. 

100 

10,  29 

siv 

157 
175 

:jo 


PniigiiqiiaK,  N.  Y.,  contact  of  old  gneiss  and  Cam- 
brian quartzite  at 21i 

PunipeUy,  K.,  cited 182 

Putnam.  B.  T.,  work  of xiii-xiv.  8, 10,21 

(Quarry  bill.  New  Asbford,  exposures  at 138, 139,  UO 

Ragged  mountain,  location  of 135 

topography  and  structure  of iSO,  170,  171.175,170 

Renard,  A.,  cited 183 

Reusch,  H.,  cited 143, 102 

Richthofen,  F.  von,  cited 27 

Riggs,  R.  B.,  analysis  of  felds]>ar  by GO,  186-187 

Rosenbusch,  H.,  cited 63 

Rowe  schist,  doubtful  age  of ■ 29 

place  of 30 

area  of 65 

Saddle  Ball,  location  and  height  of 135 

Savoy  Center,  outcrop  of  white  gneiss  conglomerate 

near 79 

Savoy  Hollow,  outcrops  near 78, 79 

Southwick  creek,  stratigraphy  on 77 

Spruce  hill,  exposures  near 86-87,88 

Stamford,  Vt.,  expi>sures  near 98-102 

contact  of  Stamford  gneiss  and  Vermont  quartz- 
ite at 100, 101 

dike  in 11 

Stamford  gneiss,  description  of 45-48 

fossils  of 51 

exposures  of,  in  Eoosac  tunnel 69,72 

contact  of,  with  conglomerate  of  Vermont  for- 
mation       73, 100 

Stockbridge  limestone,  syncline  of,  in  Cheshire 15 

thickness  of 20 

description  of 64-65 


Page. 
Stockbridge  limestone— Continued. 

exposures  of,  in  Hoosac  tunnel 69.72 

exposures  of 84,  87, 89,  98 

age  and  character  of 179, 181-182 

Stockbridge  limestone  and  Hoosac  schist,  zone  of 

''lateral  transition  between 15,  17 

Stone  bill,  geology  and  topography  of 197-201 

Strata  of  Mount  Greylock.  table 190 

Stratiiicalion  and  cleavage  foliations,  relations  of. 

at  Mount  Greylock 136,137 

Stratification  foliation,  character  of 158 

Sugar  loaf  mountain,  strata  at 140, 141 

structure  of 173 

Symonds  peak  (Mount  Prospect),  structure  of 162-163 

Tacnnic  mountains  described 6 

Topbet  creek,  exposures  of  Hoosac  schist  on.   81-82 

exposures  of  rocks  of  Vermont  formaticui  on 84.  H5 

Topographic  work  on   Hoosac  mountain,  methods 

of 41 

Topography  and  geology,  relations  of 192-196 

Vermont  formation  described 48-59 

exposures  of,  in  Hoosac^  tunnel 69,  72 

exposures  of 72,  82-88,  88-90,  94 

contact  of,  with  Stamfoi'fl  gneiss 73 

age  and  character  of , 179,  200-201 

Vermont  quartzite  and  Stockbridge  limestone,  fea- 
tures of  contact  of 95-96 

Walcott,  C.  D.,  aid  by xiv.  10, 29 

fossils  found  in  Stamford  gneiss  by 51 

cited 163. 190, 191 

Whittle,  C.  L.,  aid  by xiv 

Winchell.  A ..  cited 58 

Windsor,  Vt  .exposures  at 96 

Windsor  hill,  exposures  at 88 

Wolfl;  J.  E  ,  wtuk  of xiii.  8, 10, 11, 14, 28, 125 

cited 164, 171. 183, 187, 191 

quoted  on  microscopic    sections  of  Stone  bill 

rocks 200 

Vokura,  Mr.,  aid  by xiv 


